Systems, methods, and apparatus for detection of metal objects in a predetermined space

ABSTRACT

This disclosure provides systems, methods and apparatus for detecting foreign objects. In one aspect an apparatus for detecting a presence of an object is provided. The apparatus includes a resonant circuit having a resonant frequency. The resonant circuit includes a sense circuit including an electrically conductive structure. The apparatus further includes a coupling circuit coupled to the sense circuit. The apparatus further includes a detection circuit coupled to the sense circuit via the coupling circuit. The detection circuit is configured to detect the presence of the object in response to detecting a difference between a measured characteristic that depends on a frequency at which the resonant circuit is resonating and a corresponding characteristic that depends on the resonant frequency of the resonant circuit. The coupling circuit is configured to reduce a variation of the resonant frequency by the detection circuit in the absence of the object.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit under 35 U.S.C.§119(e) of U.S. Provisional Patent Application No. 61/671,498 entitled“SYSTEMS, METHODS, AND APPARATUS FOR DETECTION OF METAL OBJECTS IN APREDETERMINED SPACE” filed on Jul. 13, 2012, the disclosure of which ishereby incorporated by reference in its entirety.

FIELD

The present disclosure relates generally to wireless power transfer, andmore specifically to devices, systems, and methods related to wirelesspower transfer to remote systems such as vehicles including batteries.More specifically the present disclosure relates to the detection offoreign objects.

BACKGROUND

Remote systems, such as vehicles, have been introduced that includelocomotion power derived from electricity received from an energystorage device such as a battery. For example, hybrid electric vehiclesinclude on-board chargers that use power from vehicle braking andtraditional motors to charge the vehicles. Vehicles that are solelyelectric generally receive the electricity for charging the batteriesfrom other sources. Battery electric vehicles (electric vehicles) areoften proposed to be charged through some type of wired alternatingcurrent (AC) such as household or commercial AC supply sources. Thewired charging connections require cables or other similar connectorsthat are physically connected to a power supply. Cables and similarconnectors may sometimes be inconvenient or cumbersome and have otherdrawbacks. Wireless charging systems that are capable of transferringpower in free space (e.g., via a wireless field) to be used to chargeelectric vehicles may overcome some of the deficiencies of wiredcharging solutions. As such, wireless charging systems and methods thatefficiently and safely transfer power for charging electric vehicles aredesirable.

SUMMARY

Various implementations of systems, methods and devices within the scopeof the appended claims each have several aspects, no single one of whichis solely responsible for the desirable attributes described herein.Without limiting the scope of the appended claims, some prominentfeatures are described herein.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale.

One aspect of the disclosure provides an apparatus for detecting apresence of an object. The apparatus includes a resonant circuit havinga resonant frequency. The resonant circuit includes a sense circuitincluding an electrically conductive structure. The apparatus furtherincludes a coupling circuit coupled to the sense circuit. The apparatusfurther includes a detection circuit coupled to the sense circuit viathe coupling circuit. The detection circuit is configured to detect thepresence of the object in response to detecting a difference between ameasured characteristic that depends on a frequency at which theresonant circuit is resonating and a corresponding characteristic thatdepends on the resonant frequency of the resonant circuit. The couplingcircuit is configured to reduce a variation of the resonant frequency bythe detection circuit in the absence of the object.

Another aspect of the disclosure provides an implementation of a methodfor detecting a presence of an object. The method includes applying asignal to a resonant circuit having a resonant frequency. The resonantcircuit includes a sense circuit including an electrically conductivestructure. A coupling circuit is coupled to the sense circuit. Themethod further includes detecting the presence of the object via adetection circuit coupled to the sense circuit via the coupling circuitin response to detecting a difference between a measured characteristicthat depends on a frequency at which the resonant circuit is resonatingand a corresponding characteristic that depends on the resonantfrequency of the resonant circuit. The coupling circuit is configured toreduce a variation of the resonant frequency by the detection circuit inthe absence of the object.

Yet another aspect of the disclosure provides an apparatus for detectinga presence of an object. The apparatus includes means for resonating ata resonant frequency. The apparatus further includes means for detectingthe presence of the object in response to detecting a difference betweena measured characteristic that depends on a frequency at which theresonating means is resonating and a corresponding characteristic thatdepends on the resonant frequency of the resonating means. The apparatusfurther includes means for reducing variation of the resonant frequencyby the detection means in the absence of the object.

Another aspect of the subject matter described in the disclosureprovides an apparatus for detecting a presence of an object. Theapparatus includes a first sense circuit including a first electricallyconductive structure. At least the first sense circuit forms a firstresonant circuit having a first resonant frequency. The apparatusfurther includes a second sense circuit including a second electricallyconductive structure. At least the second sense circuit forms a secondresonant circuit having a second resonant frequency. The second resonantfrequency is different than the first resonant frequency. The apparatusfurther includes a detection circuit coupled to the first and secondsense circuits. The detection circuit is configured detect the presenceof the object in response to detecting a difference between a firstmeasured characteristic that depends on a frequency at which the firstresonant circuit is resonating and a first corresponding characteristicthat depends on the first resonant frequency, or a difference between asecond measured characteristic that depends on a frequency at which thesecond resonant circuit is resonating and a second correspondingcharacteristic that depends on the second resonant frequency.

Another aspect of the subject matter described in the disclosureprovides an implementation of a method for detecting a presence of anobject. The method includes applying a first signal to a first sensecircuit including a first electrically conductive structure. At leastthe first sense circuit forms a first resonant circuit having a firstresonant frequency. The method further includes applying a second signalto a second sense circuit including a second electrically conductivestructure. At least the second sense circuit forms a second resonantcircuit having a second resonant frequency. The second resonantfrequency is different than the first resonant frequency. The methodfurther includes detecting the presence of the object via a detectioncircuit in response to detecting a difference between a first measuredcharacteristic that depends on a frequency at which the first resonantcircuit is resonating and a first corresponding characteristic thatdepends on the first resonant frequency or a difference between a secondmeasured characteristic that depends on a frequency at which the secondresonant circuit is resonating and a second corresponding characteristicthat depends on the second resonant frequency.

Another aspect of the subject matter described in the disclosureprovides an apparatus for detecting a presence of an object. Theapparatus includes a first means for resonating at a first resonantfrequency. The apparatus further includes a second means for resonatingat a second resonant frequency. The second resonant frequency isdifferent than the first resonant frequency. The apparatus furtherincludes means for detecting the presence of the object in response todetecting a difference between a first measured characteristic thatdepends on a frequency at which the first resonating means is resonatingand a first corresponding characteristic that depends on the firstresonant frequency or a difference between a second measuredcharacteristic that depends on a frequency at which the secondresonating means is resonating and a second corresponding characteristicthat depends on the second resonant frequency.

Another aspect of the subject matter described in the disclosureprovides an apparatus for detecting a presence of an object in amagnetic field. The apparatus includes a power circuit configured togenerate the magnetic field and transfer power wirelessly at a levelsufficient to power or charge a load via the magnetic field. Themagnetic field causes a vibration of the object. The apparatus furtherincludes a detection circuit configured to transmit signals and detect,based on a reflection of the transmitted signals, a frequency of thevibration of the object caused by the magnetic field.

Another aspect of the subject matter described in the disclosureprovides an implementation of a method for detecting a presence of anobject in a magnetic field. The method includes generating the magneticfield and transferring power wirelessly at a level sufficient to poweror charge a load via the magnetic field. The magnetic field causes avibration of the object. The method further includes transmittingsignals and detecting, based on a reflection of the transmitted signals,a frequency of the vibration of the object caused by the magnetic field.

Another aspect of the subject matter described in the disclosureprovides an apparatus for detecting a presence of an object in amagnetic field. The apparatus includes means for generating the magneticfield and transferring power wirelessly at a level sufficient to poweror charge a load via the magnetic field. The magnetic field causes avibration of the object. The apparatus further includes means fortransmitting signals and means for detecting, based on a reflection ofthe transmitted signals, a frequency of the vibration of the objectcaused by the magnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary wireless power transfer system forcharging an electric vehicle, in accordance with an exemplaryembodiment.

FIG. 2 is a schematic diagram of exemplary core components of thewireless power transfer system of FIG. 1.

FIG. 3 is another functional block diagram showing exemplary core andancillary components of the wireless power transfer system of FIG. 1.

FIG. 4 is a functional block diagram showing a replaceable contactlessbattery disposed in an electric vehicle, in accordance with an exemplaryembodiment.

FIGS. 5A, 5B, 5C, and 5D are diagrams of exemplary configurations forthe placement of an induction coil and ferrite material relative to abattery, in accordance with exemplary embodiments.

FIG. 6 is a chart of a frequency spectrum showing exemplary frequenciesthat may be available for wireless charging an electric vehicle, inaccordance with an exemplary embodiment.

FIG. 7 is a chart showing exemplary frequencies and transmissiondistances that may be useful in wireless charging electric vehicles, inaccordance with an exemplary embodiment.

FIGS. 8A, 8B, and 8C are diagrams of portions of exemplary objectdetection circuitry, in accordance with exemplary embodiments.

FIG. 9 is a side view of a sense loop configured to detect an objectembedded within a magnetic pad, in accordance with an embodiment.

FIG. 10 is a diagram of a portion of exemplary object detectioncircuitry for detecting an object located at different positionsrelative to a sense loop, in accordance with an exemplary embodiment.

FIGS. 11A, 11B, and 11C are diagrams of different exemplaryconfigurations for sense loops configured to detect an object, inaccordance with exemplary embodiments.

FIG. 12 is a functional block diagram of an exemplary circuit configuredto detect an object based on magnetic field sensing, in accordance withexemplary embodiments.

FIG. 13 is a functional block diagram of an exemplary circuit configuredto detect an object based on sense loop impedance measurements, inaccordance with exemplary embodiments.

FIG. 14A is a functional block diagram of an exemplary circuitconfigured to detect an object based on sense loop resonant frequencymeasurements, in accordance with exemplary embodiments.

FIG. 14B is a functional block diagram of an exemplary circuitconfigured to detect an object based on sense loop resonant frequencymeasurements, in accordance with an embodiment.

FIG. 15 is another functional block diagram of an exemplary circuitconfigured to detect an object based on sense loop resonant frequencymeasurements, in accordance with exemplary embodiments.

FIG. 16 is another functional block diagram of an exemplary circuitconfigured to detect an object based on sense loop resonant frequencymeasurements, in accordance with exemplary embodiments.

FIGS. 17A, 17B, and 17C are diagrams of exemplary weakly coupledresonant sense loop configurations, in accordance with exemplaryembodiments.

FIGS. 18A and 18B are schematic diagrams of equivalent circuits of anexemplary inductively coupled resonant sense loop, in accordance with anexemplary embodiment.

FIG. 19 is a functional block diagram of an exemplary circuit configuredto detect an object using a coupling circuit between a detection circuitand a sense circuit, in accordance with an exemplary embodiment.

FIG. 20 is a functional block diagram of a circuit as shown in FIG. 19where the detection circuit is inductively coupled with a sense circuitvia a coupling loop, in accordance with an exemplary embodiment.

FIG. 21 is a functional block diagram of a circuit as shown in FIG. 19where the detection circuit is capacitively coupled with a sensecircuit, in accordance with an exemplary embodiment.

FIG. 22 is a functional block diagram of an exemplary circuit configuredto detect an object using a plurality of coupling circuits between adetection circuit and plurality of sense circuits, in accordance with anexemplary embodiment.

FIG. 23 is a functional block diagram of an exemplary circuit configuredto detect an object using a plurality of sense circuits configured tohave different resonant frequencies, in accordance with an exemplaryembodiment.

FIG. 24 is a functional block diagram of a circuit as shown in FIG. 23where the detection circuit is inductively coupled to sense circuitshaving different resonant frequencies, in accordance with an exemplaryembodiment.

FIGS. 25A, 25B, 25C, 25D, 25E, and 25F are diagrams of exemplaryconfigurations sense loop arrays inductively or capacitivley coupled toa detection circuit, in accordance with an exemplary embodiment.

FIGS. 26A, 26B, 26C, 26D, 26E, and 26F are schematic diagrams ofexemplary equivalent circuits of inductively or capacitively coupledresonant loop arrays, in accordance with an exemplary embodiment.

FIG. 27 is a plot showing a phase response of an inductively coupledresonant loop array before and after compensating for an impedance of acoupling loop, in accordance with an exemplary embodiment.

FIG. 28 is a functional block diagram of an exemplary circuit fordetecting an object integrated within a inductive charging padconfigured to wirelessly transmit power, in accordance with an exemplaryembodiment.

FIG. 29 is a functional block diagram of an exemplary inductivelycoupled resonant filter for detecting an object, in accordance with anexemplary embodiment.

FIG. 30A is a functional block diagram of another exemplary system fordetecting an object, in accordance with an exemplary embodiment.

FIG. 30B is a functional block diagram of a detection circuit of thesystem of FIG. 30A, in accordance with an exemplary embodiment.

FIG. 31 is a flowchart of an exemplary method for detecting the presenceof an object, in accordance with an exemplary embodiment.

FIG. 32 is a functional block diagram of an apparatus for detecting thepresence of an object, in accordance with an exemplary embodiment.

FIG. 33 is a flowchart of an exemplary method for detecting the presenceof an object in a magnetic field, in accordance with an exemplaryembodiment.

FIG. 34 is a functional block diagram of an apparatus for detecting thepresence of an object in a magnetic field, in accordance with anexemplary embodiment.

The various features illustrated in the drawings may not be drawn toscale. Accordingly, the dimensions of the various features may bearbitrarily expanded or reduced for clarity. In addition, some of thedrawings may not depict all of the components of a given system, methodor device. Finally, like reference numerals may be used to denote likefeatures throughout the specification and figures.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments and isnot intended to represent the only embodiments in which the inventionmay be practiced. The term “exemplary” used throughout this descriptionmeans “serving as an example, instance, or illustration,” and should notnecessarily be construed as preferred or advantageous over otherexemplary embodiments. The detailed description includes specificdetails for the purpose of providing a thorough understanding of theexemplary embodiments. In some instances, some devices are shown inblock diagram form.

Wirelessly transferring power may refer to transferring any form ofenergy associated with electric fields, magnetic fields, electromagneticfields, or otherwise from a transmitter to a receiver without the use ofphysical electrical conductors (e.g., power may be transferred throughfree space). The power output into a wireless field (e.g., a magneticfield) may be received, captured by, or coupled by a “receiving coil” toachieve power transfer.

An electric vehicle is used herein to describe a remote system, anexample of which is a vehicle that includes, as part of its locomotioncapabilities, electrical power derived from a chargeable energy storagedevice (e.g., one or more rechargeable electrochemical cells or othertype of battery). As non-limiting examples, some electric vehicles maybe hybrid electric vehicles that include besides electric motors, atraditional combustion engine for direct locomotion or to charge thevehicle's battery. Other electric vehicles may draw all locomotionability from electrical power. An electric vehicle is not limited to anautomobile and may include motorcycles, carts, scooters, and the like.By way of example and not limitation, a remote system is describedherein in the form of an electric vehicle (EV). Furthermore, otherremote systems that may be at least partially powered using a chargeableenergy storage device are also contemplated (e.g., electronic devicessuch as personal computing devices and the like).

FIG. 1 is a diagram of an exemplary wireless power transfer system 100for charging an electric vehicle 112, in accordance with an exemplaryembodiment. The wireless power transfer system 100 enables charging ofan electric vehicle 112 while the electric vehicle 112 is parked near abase wireless charging system 102 a. Spaces for two electric vehiclesare illustrated in a parking area to be parked over corresponding basewireless charging system 102 a and 102 b. In some embodiments, a localdistribution center 130 may be connected to a power backbone 132 andconfigured to provide an alternating current (AC) or a direct current(DC) supply through a power link 110 to the base wireless chargingsystem 102 a. The base wireless charging system 102 a also includes abase system induction coil 104 a for wirelessly transferring orreceiving power. An electric vehicle 112 may include a battery unit 118,an electric vehicle induction coil 116, and an electric vehicle wirelesscharging system 114. The electric vehicle induction coil 116 mayinteract with the base system induction coil 104 a for example, via aregion of the electromagnetic field generated by the base systeminduction coil 104 a.

In some exemplary embodiments, the electric vehicle induction coil 116may receive power when the electric vehicle induction coil 116 islocated in an energy field produced by the base system induction coil104 a. The field corresponds to a region where energy output by the basesystem induction coil 104 a may be captured by an electric vehicleinduction coil 116. For example, the energy output by the base systeminduction coil 104 a may be at a level sufficient to charge or power theelectric vehicle 112. In some cases, the field may correspond to the“near field” of the base system induction coil 104 a. The near-field maycorrespond to a region in which there are strong reactive fieldsresulting from the currents and charges in the base system inductioncoil 104 a that do not radiate power away from the base system inductioncoil 104 a. In some cases the near-field may correspond to a region thatis within about ½π of wavelength of the base system induction coil 104 a(and vice versa for the electric vehicle induction coil 116) as will befurther described below.

Local distribution 1130 may be configured to communicate with externalsources (e.g., a power grid) via a communication backhaul 134, and withthe base wireless charging system 102 a via a communication link 108.

In some embodiments the electric vehicle induction coil 116 may bealigned with the base system induction coil 104 a and, therefore,disposed within a near-field region simply by the driver positioning theelectric vehicle 112 correctly relative to the base system inductioncoil 104 a. In other embodiments, the driver may be given visualfeedback, auditory feedback, or combinations thereof to determine whenthe electric vehicle 112 is properly placed for wireless power transfer.In yet other embodiments, the electric vehicle 112 may be positioned byan autopilot system, which may move the electric vehicle 112 back andforth (e.g., in zig-zag movements) until an alignment error has reacheda tolerable value. This may be performed automatically and autonomouslyby the electric vehicle 112 without or with only minimal driverintervention provided that the electric vehicle 112 is equipped with aservo steering wheel, ultrasonic sensors, and intelligence to adjust thevehicle. In still other embodiments, the electric vehicle induction coil116, the base system induction coil 104 a, or a combination thereof mayhave functionality for displacing and moving the induction coils 116 and104 a relative to each other to more accurately orient them and developmore efficient coupling therebetween.

The base wireless charging system 102 a may be located in a variety oflocations. As non-limiting examples, some suitable locations include aparking area at a home of the electric vehicle 112 owner, parking areasreserved for electric vehicle wireless charging modeled afterconventional petroleum-based filling stations, and parking lots at otherlocations such as shopping centers and places of employment.

Charging electric vehicles wirelessly may provide numerous benefits. Forexample, charging may be performed automatically, virtually withoutdriver intervention and manipulations thereby improving convenience to auser. There may also be no exposed electrical contacts and no mechanicalwear out, thereby improving reliability of the wireless power transfersystem 100. Manipulations with cables and connectors may not be needed,and there may be no cables, plugs, or sockets that may be exposed tomoisture and water in an outdoor environment, thereby improving safety.There may also be no sockets, cables, and plugs visible or accessible,thereby reducing potential vandalism of power charging devices. Further,since an electric vehicle 112 may be used as distributed storage devicesto stabilize a power grid, a docking-to-grid solution may be used toincrease availability of vehicles for Vehicle-to-Grid (V2G) operation.

A wireless power transfer system 100 as described with reference to FIG.1 may also provide aesthetical and non-impedimental advantages. Forexample, there may be no charge columns and cables that may beimpedimental for vehicles and/or pedestrians.

As a further explanation of the vehicle-to-grid capability, the wirelesspower transmit and receive capabilities may be configured to bereciprocal such that the base wireless charging system 102 a transferspower to the electric vehicle 112 and the electric vehicle 112 transferspower to the base wireless charging system 102 a e.g., in times ofenergy shortfall. This capability may be useful to stabilize the powerdistribution grid by allowing electric vehicles to contribute power tothe overall distribution system in times of energy shortfall caused byover demand or shortfall in renewable energy production (e.g., wind orsolar).

FIG. 2 is a schematic diagram of exemplary core components of thewireless power transfer system 100 of FIG. 1. As shown in FIG. 2, thewireless power transfer system 200 may include a base system transmitcircuit 206 including a base system induction coil 204 having aninductance L₁. The wireless power transfer system 200 further includesan electric vehicle receive circuit 222 including an electric vehicleinduction coil 216 having an inductance L₂. Embodiments described hereinmay use capacitively loaded wire loops (i.e., multi-turn coils) forminga resonant structure that is capable of efficiently coupling energy froma primary structure (transmitter) to a secondary structure (receiver)via a magnetic or electromagnetic near field if both primary andsecondary are tuned to a common resonant frequency. The coils may beused for the electric vehicle induction coil 216 and the base systeminduction coil 204. Using resonant structures for coupling energy may bereferred to “magnetic coupled resonance,” “electromagnetic coupledresonance,” and/or “resonant induction.” The operation of the wirelesspower transfer system 200 will be described based on power transfer froma base wireless power charging system 202 to an electric vehicle 112,but is not limited thereto. For example, as discussed above, theelectric vehicle 112 may transfer power to the base wireless chargingsystem 102 a.

With reference to FIG. 2, a power supply 208 (e.g., AC or DC) suppliespower P_(SDC) to the base wireless power charging system 202 to transferenergy to an electric vehicle 112. The base wireless power chargingsystem 202 includes a base charging system power converter 236. The basecharging system power converter 236 may include circuitry such as anAC/DC converter configured to convert power from standard mains AC to DCpower at a suitable voltage level, and a DC/low frequency (LF) converterconfigured to convert DC power to power at an operating frequencysuitable for wireless high power transfer. The base charging systempower converter 236 supplies power P₁ to the base system transmitcircuit 206 including the capacitor C₁ in series with the base systeminduction coil 204 to emit an electromagnetic field at a desiredfrequency. The capacitor C₁ may be coupled with the base systeminduction coil 204 either in parallel or in series, or may be formed ofseveral reactive elements in any combination of parallel or seriestopology. The capacitor C₁ may be provided to form a resonant circuitwith the base system induction coil 204 that resonates at a desiredfrequency. The base system induction coil 204 receives the power P₁ andwirelessly transmits power at a level sufficient to charge or power theelectric vehicle 112. For example, the power level provided wirelesslyby the base system induction coil 204 may be on the order of kilowatts(kW) (e.g., anywhere from 1 kW to 110 kW or higher or lower).

The base system transmit circuit 206 including the base system inductioncoil 204 and electric vehicle receive circuit 222 including the electricvehicle induction coil 216 may be tuned to substantially the samefrequencies and may be positioned within the near-field of anelectromagnetic field transmitted by one of the base system inductioncoil 204 and the electric vehicle induction coil 116. In this case, thebase system induction coil 204 and electric vehicle induction coil 116may become coupled to one another such that power may be transferred tothe electric vehicle receive circuit 222 including capacitor C₂ andelectric vehicle induction coil 116. The capacitor C₂ may be provided toform a resonant circuit with the electric vehicle induction coil 216that resonates at a desired frequency. The capacitor C₂ may be coupledwith the electric vehicle induction coil 204 either in parallel or inseries, or may be formed of several reactive elements in any combinationof parallel or series topology. Element k(d) represents the mutualcoupling coefficient resulting at coil separation. Equivalentresistances R_(eq,1) and R_(eq,2) represent the losses that may beinherent to the induction coils 204 and 216 and the anti-reactancecapacitors C₁ and C₂. The electric vehicle receive circuit 222 includingthe electric vehicle induction coil 316 and capacitor C₂ receives powerP₂ and provides the power P₂ to an electric vehicle power converter 238of an electric vehicle charging system 214.

The electric vehicle power converter 238 may include, among otherthings, a LF/DC converter configured to convert power at an operatingfrequency back to DC power at a voltage level matched to the voltagelevel of an electric vehicle battery unit 218. The electric vehiclepower converter 238 may provide the converted power P_(LDC) to chargethe electric vehicle battery unit 218. The power supply 208, basecharging system power converter 236, and base system induction coil 204may be stationary and located at a variety of locations as discussedabove. The battery unit 218, electric vehicle power converter 238, andelectric vehicle induction coil 216 may be included in an electricvehicle charging system 214 that is part of electric vehicle 112 or partof the battery pack (not shown). The electric vehicle charging system214 may also be configured to provide power wirelessly through theelectric vehicle induction coil 216 to the base wireless power chargingsystem 202 to feed power back to the grid. Each of the electric vehicleinduction coil 216 and the base system induction coil 204 may act astransmit or receive induction coils based on the mode of operation.

While not shown, the wireless power transfer system 200 may include aload disconnect unit (LDU) to safely disconnect the electric vehiclebattery unit 218 or the power supply 208 from the wireless powertransfer system 200. For example, in case of an emergency or systemfailure, the LDU may be triggered to disconnect the load from thewireless power transfer system 200. The LDU may be provided in additionto a battery management system for managing charging to a battery, or itmay be part of the battery management system.

Further, the electric vehicle charging system 214 may include switchingcircuitry (not shown) for selectively connecting and disconnecting theelectric vehicle induction coil 216 to the electric vehicle powerconverter 238. Disconnecting the electric vehicle induction coil 216 maysuspend charging and also may adjust the “load” as “seen” by the basewireless charging system 102 a (acting as a transmitter), which may beused to “cloak” the electric vehicle charging system 114 (acting as thereceiver) from the base wireless charging system 102 a. The load changesmay be detected if the transmitter includes the load sensing circuit.Accordingly, the transmitter, such as a base wireless charging system202, may have a mechanism for determining when receivers, such as anelectric vehicle charging system 114, are present in the near-field ofthe base system induction coil 204.

As described above, in operation, assuming energy transfer towards thevehicle or battery, input power is provided from the power supply 208such that the base system induction coil 204 generates a field forproviding the energy transfer. The electric vehicle induction coil 216couples to the radiated field and generates output power for storage orconsumption by the electric vehicle 112. As described above, in someembodiments, the base system induction coil 204 and electric vehicleinduction coil 116 are configured according to a mutual resonantrelationship such that when the resonant frequency of the electricvehicle induction coil 116 and the resonant frequency of the base systeminduction coil 204 are very close or substantially the same.Transmission losses between the base wireless power charging system 202and electric vehicle charging system 214 are minimal when the electricvehicle induction coil 216 is located in the near-field of the basesystem induction coil 204.

As stated, an efficient energy transfer occurs by coupling a largeportion of the energy in the near field of a transmitting induction coilto a receiving induction coil rather than propagating most of the energyin an electromagnetic wave to the far-field. When in the near field, acoupling mode may be established between the transmit induction coil andthe receive induction coil. The area around the induction coils wherethis near field coupling may occur is referred to herein as a near fieldcoupling mode region.

While not shown, the base charging system power converter 236 and theelectric vehicle power converter 238 may both include an oscillator, adriver circuit such as a power amplifier, a filter, and a matchingcircuit for efficient coupling with the wireless power induction coil.The oscillator may be configured to generate a desired frequency, whichmay be adjusted in response to an adjustment signal. The oscillatorsignal may be amplified by a power amplifier with an amplificationamount responsive to control signals. The filter and matching circuitmay be included to filter out harmonics or other unwanted frequenciesand match the impedance of the power conversion module to the wirelesspower induction coil. The power converters 236 and 238 may also includea rectifier and switching circuitry to generate a suitable power outputto charge the battery.

The electric vehicle induction coil 216 and base system induction coil204 as described throughout the disclosed embodiments may be referred toor configured as “loop” antennas, and more specifically, multi-turn loopantennas. The induction coils 204 and 216 may also be referred to hereinor be configured as “magnetic” antennas. The term “coils” is intended torefer to a component that may wirelessly output or receive energy fourcoupling to another “coil.” The coil may also be referred to as an“antenna” of a type that is configured to wirelessly output or receivepower. As used herein, coils 204 and 216 are examples of “power transfercomponents” of a type that are configured to wirelessly output,wirelessly receive, and/or wirelessly relay power. Loop (e.g.,multi-turn loop) antennas may be configured to include an air core or aphysical core such as a ferrite core. An air core loop antenna may allowthe placement of other components within the core area. Physical coreantennas including ferromagnetic or ferromagnetic materials may allowdevelopment of a stronger electromagnetic field and improved coupling.

As discussed above, efficient transfer of energy between a transmitterand receiver occurs during matched or nearly matched resonance between atransmitter and a receiver. However, even when resonance between atransmitter and receiver are not matched, energy may be transferred at alower efficiency. Transfer of energy occurs by coupling energy from thenear field of the transmitting induction coil to the receiving inductioncoil residing within a region (e.g., within a predetermined frequencyrange of the resonant frequency, or within a predetermined distance ofthe near-field region) where this near field is established rather thanpropagating the energy from the transmitting induction coil into freespace.

A resonant frequency may be based on the inductance and capacitance of atransmit circuit including an induction coil (e.g., the base systeminduction coil 204) as described above. As shown in FIG. 2, inductancemay generally be the inductance of the induction coil, whereas,capacitance may be added to the induction coil to create a resonantstructure at a desired resonant frequency. As a non-limiting example, asshown in FIG. 2, a capacitor may be added in series with the inductioncoil to create a resonant circuit (e.g., the base system transmitcircuit 206) that generates an electromagnetic field. Accordingly, forlarger diameter induction coils, the value of capacitance needed toinduce resonance may decrease as the diameter or inductance of the coilincreases. Inductance may also depend on a number of turns of aninduction coil. Furthermore, as the diameter of the induction coilincreases, the efficient energy transfer area of the near field mayincrease. Other resonant circuits are possible. As another non limitingexample, a capacitor may be placed in parallel between the two terminalsof the induction coil (e.g., a parallel resonant circuit). Furthermorean induction coil may be designed to have a high quality (Q) factor toimprove the resonance of the induction coil. For example, the Q factormay be 300 or greater.

As described above, according to some embodiments, coupling powerbetween two induction coils that are in the near field of one another isdisclosed. As described above, the near field may correspond to a regionaround the induction coil in which electromagnetic fields exist but maynot propagate or radiate away from the induction coil. Near-fieldcoupling-mode regions may correspond to a volume that is near thephysical volume of the induction coil, typically within a small fractionof the wavelength. According to some embodiments, electromagneticinduction coils, such as single and multi-turn loop antennas, are usedfor both transmitting and receiving since magnetic near field amplitudesin practical embodiments tend to be higher for magnetic type coils incomparison to the electric near fields of an electric type antenna(e.g., a small dipole). This allows for potentially higher couplingbetween the pair. Furthermore, “electric” antennas (e.g., dipoles andmonopoles) or a combination of magnetic and electric antennas may beused.

FIG. 3 is another functional block diagram showing exemplary core andancillary components of the wireless power transfer system 300 ofFIG. 1. The wireless power transfer system 300 illustrates acommunication link 376, a guidance link 366, and alignment systems 352,354 for the base system induction coil 304 and electric vehicleinduction coil 316. As described above with reference to FIG. 2, andassuming energy flow towards the electric vehicle 112, in FIG. 3 a basecharging system power interface 354 may be configured to provide powerto a charging system power converter 336 from a power source, such as anAC or DC power supply 126. The base charging system power converter 336may receive AC or DC power from the base charging system power interface354 to excite the base system induction coil 304 at or near its resonantfrequency. The electric vehicle induction coil 316, when in the nearfield coupling-mode region, may receive energy from the near fieldcoupling mode region to oscillate at or near the resonant frequency. Theelectric vehicle power converter 338 converts the oscillating signalfrom the electric vehicle induction coil 316 to a power signal suitablefor charging a battery via the electric vehicle power interface.

The base wireless charging system 302 includes a base charging systemcontroller 342 and the electric vehicle charging system 314 includes anelectric vehicle controller 344. The base charging system controller 342may include a base charging system communication interface 162 to othersystems (not shown) such as, for example, a computer, and a powerdistribution center, or a smart power grid. The electric vehiclecontroller 344 may include an electric vehicle communication interfaceto other systems (not shown) such as, for example, an on-board computeron the vehicle, other battery charging controller, other electronicsystems within the vehicles, and remote electronic systems.

The base charging system controller 342 and electric vehicle controller344 may include subsystems or modules for specific application withseparate communication channels. These communications channels may beseparate physical channels or separate logical channels. As non-limitingexamples, a base charging alignment system 352 may communicate with anelectric vehicle alignment system 354 through a communication link 376to provide a feedback mechanism for more closely aligning the basesystem induction coil 304 and electric vehicle induction coil 316,either autonomously or with operator assistance. Similarly, a basecharging guidance system 362 may communicate with an electric vehicleguidance system 364 through a guidance link to provide a feedbackmechanism to guide an operator in aligning the base system inductioncoil 304 and electric vehicle induction coil 316. In addition, there maybe separate general-purpose communication links (e.g., channels)supported by base charging communication system 372 and electric vehiclecommunication system 374 for communicating other information between thebase wireless power charging system 302 and the electric vehiclecharging system 314. This information may include information aboutelectric vehicle characteristics, battery characteristics, chargingstatus, and power capabilities of both the base wireless power chargingsystem 302 and the electric vehicle charging system 314, as well asmaintenance and diagnostic data for the electric vehicle 112. Thesecommunication channels may be separate physical communication channelssuch as, for example, Bluetooth, zigbee, cellular, etc.

Electric vehicle controller 344 may also include a battery managementsystem (BMS) (not shown) that manages charge and discharge of theelectric vehicle principal battery, a parking assistance system based onmicrowave or ultrasonic radar principles, a brake system configured toperform a semi-automatic parking operation, and a steering wheel servosystem configured to assist with a largely automated parking ‘park bywire’ that may provide higher parking accuracy, thus reducing the needfor mechanical horizontal induction coil alignment in any of the basewireless charging system 102 a and the electric vehicle charging system114. Further, electric vehicle controller 344 may be configured tocommunicate with electronics of the electric vehicle 112. For example,electric vehicle controller 344 may be configured to communicate withvisual output devices (e.g., a dashboard display), acoustic/audio outputdevices (e.g., buzzer, speakers), mechanical input devices (e.g.,keyboard, touch screen, and pointing devices such as joystick,trackball, etc.), and audio input devices (e.g., microphone withelectronic voice recognition).

Furthermore, the wireless power transfer system 300 may includedetection and sensor systems. For example, the wireless power transfersystem 300 may include sensors for use with systems to properly guidethe driver or the vehicle to the charging spot, sensors to mutuallyalign the induction coils with the required separation/coupling, sensorsto detect objects that may obstruct the electric vehicle induction coil316 from moving to a particular height and/or position to achievecoupling, and safety sensors for use with systems to perform a reliable,damage free, and safe operation of the system. For example, a safetysensor may include a sensor for detection of presence of animals orchildren approaching the wireless power induction coils 104 a, 116beyond a safety radius, detection of metal objects near the base systeminduction coil 304 that may be heated up (induction heating), detectionof hazardous events such as incandescent objects on the base systeminduction coil 304, and temperature monitoring of the base wirelesspower charging system 302 and electric vehicle charging system 314components.

The wireless power transfer system 300 may also support plug-in chargingvia a wired connection. A wired charge port may integrate the outputs ofthe two different chargers prior to transferring power to or from theelectric vehicle 112. Switching circuits may provide the functionalityas needed to support both wireless charging and charging via a wiredcharge port.

To communicate between a base wireless charging system 302 and anelectric vehicle charging system 314, the wireless power transfer system300 may use both in-band signaling and an RF data modem (e.g., Ethernetover radio in an unlicensed band). The out-of-band communication mayprovide sufficient bandwidth for the allocation of value-add services tothe vehicle user/owner. A low depth amplitude or phase modulation of thewireless power carrier may serve as an in-band signaling system withminimal interference.

In addition, some communication may be performed via the wireless powerlink without using specific communications antennas. For example, thewireless power induction coils 304 and 316 may also be configured to actas wireless communication transmitters. Thus, some embodiments of thebase wireless power charging system 302 may include a controller (notshown) for enabling keying type protocol on the wireless power path. Bykeying the transmit power level (amplitude shift keying) at predefinedintervals with a predefined protocol, the receiver may detect a serialcommunication from the transmitter. The base charging system powerconverter 336 may include a load sensing circuit (not shown) fordetecting the presence or absence of active electric vehicle receiversin the vicinity of the near field generated by the base system inductioncoil 304. By way of example, a load sensing circuit monitors the currentflowing to the power amplifier, which is affected by the presence orabsence of active receivers in the vicinity of the near field generatedby base system induction coil 104 a. Detection of changes to the loadingon the power amplifier may be monitored by the base charging systemcontroller 342 for use in determining whether to enable the oscillatorfor transmitting energy, to communicate with an active receiver, or acombination thereof.

To enable wireless high power transfer, some embodiments may beconfigured to transfer power at a frequency in the range from 10-60 kHz.This low frequency coupling may allow highly efficient power conversionthat may be achieved using solid state devices. In addition, there maybe less coexistence issues with radio systems compared to other bands.

The wireless power transfer system 100 described may be used with avariety of electric vehicles 102 including rechargeable or replaceablebatteries. FIG. 4 is a functional block diagram showing a replaceablecontactless battery disposed in an electric vehicle 412, in accordancewith an exemplary embodiment. In this embodiment, the low batteryposition may be useful for an electric vehicle battery unit thatintegrates a wireless power interface (e.g., a charger-to-batterycordless interface 426) and that may receive power from a charger (notshown) embedded in the ground. In FIG. 4, the electric vehicle batteryunit may be a rechargeable battery unit, and may be accommodated in abattery compartment 424. The electric vehicle battery unit also providesa wireless power interface 426, which may integrate the entire electricvehicle wireless power subsystem including a resonant induction coil,power conversion circuitry, and other control and communicationsfunctions as needed for efficient and safe wireless energy transferbetween a ground-based wireless charging unit and the electric vehiclebattery unit.

It may be useful for the electric vehicle induction coil to beintegrated flush with a bottom side of electric vehicle battery unit orthe vehicle body so that there are no protrusive parts and so that thespecified ground-to-vehicle body clearance may be maintained. Thisconfiguration may require some room in the electric vehicle battery unitdedicated to the electric vehicle wireless power subsystem. The electricvehicle battery unit 422 may also include a battery-to-EV cordlessinterface 422, and a charger-to-battery cordless interface 426 thatprovides contactless power and communication between the electricvehicle 412 and a base wireless charging system 102 a as shown in FIG.1.

In some embodiments, and with reference to FIG. 1, the base systeminduction coil 104 a and the electric vehicle induction coil 116 may bein a fixed position and the induction coils are brought within anear-field coupling region by overall placement of the electric vehicleinduction coil 116 relative to the base wireless charging system 102 a.However, in order to perform energy transfer rapidly, efficiently, andsafely, the distance between the base system induction coil 104 a andthe electric vehicle induction coil 116 may need to be reduced toimprove coupling. Thus, in some embodiments, the base system inductioncoil 104 a and/or the electric vehicle induction coil 116 may bedeployable and/or moveable to bring them into better alignment.

FIGS. 5A, 5B, 5C, and 5D are diagrams of exemplary configurations forthe placement of an induction coil and ferrite material relative to abattery, in accordance with exemplary embodiments. FIG. 5A shows a fullyferrite embedded induction coil 536 a. The wireless power induction coilmay include a ferrite material 538 a and a coil 536 a wound about theferrite material 538 a. The coil 536 a itself may be made of strandedLitz wire. A conductive shield 532 a may be provided to protectpassengers of the vehicle from excessive EMF transmission. Conductiveshielding may be particularly useful in vehicles made of plastic orcomposites.

FIG. 5B shows an optimally dimensioned ferrite plate (i.e., ferritebacking) to enhance coupling and to reduce eddy currents (heatdissipation) in the conductive shield 532 b. The coil 536 b may be fullyembedded in a non-conducting non-magnetic (e.g., plastic) material. Forexample, as illustrated in FIG. 5A-5D, the coil 536 b may be embedded ina protective housing 534 b. There may be a separation between the coil536 b and the ferrite material 538 b as the result of a trade-offbetween magnetic coupling and ferrite hysteresis losses.

FIG. 5C illustrates another embodiment where the coil 536 c (e.g., acopper Litz wire multi-turn coil) may be movable in a lateral (“X”)direction. FIG. 5D illustrates another embodiment where the inductioncoil module is deployed in a downward direction. In some embodiments,the battery unit includes one of a deployable and non-deployableelectric vehicle induction coil module 540 d as part of the wirelesspower interface. To prevent magnetic fields from penetrating into thebattery space 530 d and into the interior of the vehicle, there may be aconductive shield 532 d (e.g., a copper sheet) between the battery space530 d and the vehicle. Furthermore, a non-conductive (e.g., plastic)protective layer 533 d may be used to protect the conductive shield 532d, the coil 536 d, and the ferrite material 5 d 38 from environmentalimpacts (e.g., mechanical damage, oxidization, etc.). Furthermore, thecoil 536 d may be movable in lateral X and/or Y directions. FIG. 5Dillustrates an embodiment wherein the electric vehicle induction coilmodule 540 d is deployed in a downward Z direction relative to a batteryunit body.

The design of this deployable electric vehicle induction coil module 542b is similar to that of FIG. 5B except there is no conductive shieldingat the electric vehicle induction coil module 542 d. The conductiveshield 532 d stays with the battery unit body. The protective layer 533d (e.g., plastic layer) is provided between the conductive shield 432 dand the electric vehicle induction coil module 542 d when the electricvehicle induction coil module 542 d is not in a deployed state. Thephysical separation of the electric vehicle induction coil module 542from the battery unit body may have a positive effect on the inductioncoil's performance.

As discussed above, the electric vehicle induction coil module 542 dthat is deployed may contain only the coil 536 d (e.g., Litz wire) andferrite material 538 d. Ferrite backing may be provided to enhancecoupling and to prevent from excessive eddy current losses in avehicle's underbody or in the conductive shield 532 d. Moreover, theelectric vehicle induction coil module 542 d may include a flexible wireconnection to power conversion electronics and sensor electronics. Thiswire bundle may be integrated into the mechanical gear for deploying theelectric vehicle induction coil module 542 d.

With reference to FIG. 1, the charging systems described above may beused in a variety of locations for charging an electric vehicle 112, ortransferring power back to a power grid. For example, the transfer ofpower may occur in a parking lot environment. It is noted that a“parking area” may also be referred to herein as a “parking space.” Toenhance the efficiency of a vehicle wireless power transfer system 100,an electric vehicle 112 may be aligned along an X direction and a Ydirection to enable an electric vehicle induction coil 116 within theelectric vehicle 112 to be adequately aligned with a base wirelesscharging system 102 a within an associated parking area.

Furthermore, the disclosed embodiments are applicable to parking lotshaving one or more parking spaces or parking areas, wherein at least oneparking space within a parking lot may comprise a base wireless chargingsystem 102 a. Guidance systems (not shown) may be used to assist avehicle operator in positioning an electric vehicle 112 in a parkingarea to align an electric vehicle induction coil 116 within the electricvehicle 112 with a base wireless charging system 102 a. Guidance systemsmay include electronic based approaches (e.g., radio positioning,direction finding principles, and/or optical, quasi-optical and/orultrasonic sensing methods) or mechanical-based approaches (e.g.,vehicle wheel guides, tracks or stops), or any combination thereof, forassisting an electric vehicle operator in positioning an electricvehicle 112 to enable an induction coil 116 within the electric vehicle112 to be adequately aligned with a charging induction coil within acharging base (e.g., base wireless charging system 102 a).

As discussed above, the electric vehicle charging system 114 may beplaced on the underside of the electric vehicle 112 for transmitting andreceiving power from a base wireless charging system 102 a. For example,an electric vehicle induction coil 116 may be integrated into thevehicles underbody preferably near a center position providing maximumsafety distance in regards to EM exposure and permitting forward andreverse parking of the electric vehicle.

FIG. 6 is a chart of a frequency spectrum showing exemplary frequenciesthat may be used for wireless charging an electric vehicle, inaccordance with an exemplary embodiment. As shown in FIG. 6, potentialfrequency ranges for wireless high power transfer to electric vehiclesmay include: VLF in a 3 kHz to 30 kHz band, lower LF in a 30 kHz to 150kHz band (for ISM-like applications) with some exclusions, HF 6.78 MHz(ITU-R ISM-Band 6.765-6.795 MHz), HF 13.56 MHz (ITU-R ISM-Band13.553-13.567), and HF 27.12 MHz (ITU-R ISM-Band 26.957-27.283).

FIG. 7 is a chart showing exemplary frequencies and transmissiondistances that may be useful in wireless charging electric vehicles, inaccordance with an exemplary embodiment. Some example transmissiondistances that may be useful for electric vehicle wireless charging areabout 30 mm, about 75 mm, and about 150 mm. Some exemplary frequenciesmay be about 27 kHz in the VLF band and about 135 kHz in the LF band.

Aspects of various embodiments described herein are directed to thedetection of objects, for example, metal objects within specifiedregion. Systems and methods for detection of metal objects as describedherein may be incorporated into the systems described above for wirelesspower transfer. For example, embodiments for detection of objects asdescribed below may be incorporated as a part of systems, such as thosedescribed above for inductive transfer of electrical energy from aprimary structure to a secondary structure across an air gap. Exemplaryfrequencies for inductive transfer of energy may be in the range from 20kHz to 150 kHz, but is not limited to this frequency range. Morespecifically, one application of the embodiments for detection ofobjects and methods described herein is inductive charging of stationaryelectric road vehicles and particularly embodiments where there is amagnetic structure (charging pad) on ground and a pick-up pad mounted atbottom side (underbody) of the vehicle. Other applications may beinductive powering or charging of electric vehicles on the move (dynamiccharging), inductive charging of portable electrical and electronicdevices, induction heating or any other systems generating strongalternating magnetic fields.

Moreover, while certain embodiments may be used in wireless powertransfer systems, it should be appreciated that the various embodimentsdescribed herein may be applicable to other applications for detectingmetal objects in a predetermined space unrelated to systems generatingalternating magnetic fields. For example, aspects of embodimentsdescribed herein may be used in antitheft detectors for detecting metalobjects that are removed from a predetermined space, security systems,quality assurance systems, electronic article surveillance, electronicarticle management, and the like.

The following acronyms may be used herein:

EMF Electro-Magnetic Field

FOD Foreign Object Detection

HF High Frequency

IF Intermediate frequency

LF Low Frequency

LMS Least Mean Square

MTBF Mean Time Between Failures

MUX Multiplexer

NCO Numerically Controlled Oscillator

PCB Printed Circuit Board

PSTN Public Switched Telephone Network

PWB Printed Wire Board

SNR Signal-to-Noise Ratio

Certain descriptions of principles, methods and embodiments describedherein refer to induction charging of electric vehicles (EV) or hybridelectric vehicles (HEV) and have to be regarded in this context. Some ofthe basic principles may be also useful for other applications asmentioned above. However, the embodiments may be modified and adapted tothe specific requirements of these applications.

With respect to induction charging, depending on the energy transferrate (power level), operating frequency, size and design of the primaryand secondary magnetic structures and the distance between them, theflux density in the air gap at some locations may exceed 0.5 mT and mayreach several Millitesla. If an object that includes a certain amount ofwell conductive material (e.g., metal) is inserted into the spacebetween the primary and secondary structures, eddy currents aregenerated in this object (Lenz's law), that may lead to powerdissipation and subsequent heating effects. This induction heatingeffect depends on the magnetic flux density, the frequency of thealternating magnetic field, the size, shape, orientation andconductivity of the object's conducting structure. When the object isexposed to the magnetic field for a sufficiently long time, it may heatup to temperatures that may be considered hazardous in regards to:

-   -   Self-ignition, if the object includes inflammable materials or        if it is in direct contact with such materials e.g., a cigarette        package including a thin metalized foil;    -   Burnings of the hand of a persons that may pick-up such a hot        object e.g., a coin or a key; or    -   Damaging the plastic enclosure of the primary or secondary        structure e.g., an object melting into the plastic.

A temperature increase may be also expected in objects includingferromagnetic materials that may be substantially non-conducting butexhibiting a pronounced hysteresis effect or in materials that generateboth hysteresis and eddy current losses. As such, detecting such objectsis beneficial to avoid corresponding harmful consequences. If the objectdetection system is integrated within a system for providing wirelesspower, in response to detecting a harmful object, the system may reducea power level or shut down until measures may be taken to remove theharmful object.

In certain applications of inductive power transfer such as charging ofelectric vehicles in domestic and public zones, it may be compulsory forreasons of safety of persons and equipment to be able to detect foreignobjects that have the potential to heat up to critical temperatures.This may be particularly true in systems where the critical space isopen and accessible such that foreign objects may get accidentally ormay be put intentionally into this space (e.g., in case of sabotage).

For example, the German VDE/DKE guideline for inductive charging ofelectric road vehicles (VDE-AR-E 2122-4-2 Elektrische Ausrüstung vonElektro-StraBenfahrzeugen—Induktive Ladung von Elektrofahrzeugen—Teil4-2: Niedriger Leistungsbereich) (hereinafter “VDE-AR-E”) e.g., definesprotection limits for thermal effects in the functional space of aninductive charging system. These limits have been chosen following aninternational standard (IEC 60364-4-42:2010-05 “Low-voltage electricalinstallations—Part 4-42: Protection for safety—Protection againstthermal effects”) on low voltage electrical installations. The Germanguideline VDE-AR-E also defines reference objects to be used forcompliance testing e.g., a

5 cent coin and an aluminum coated foil.

Embodiments described herein are directed to automatically detectinghazardous foreign objects in the following (e.g., ‘metal objects’) thatmay be located in a pre-defined space. In particular, certainembodiments are directed to detecting small metal objects (e.g., a coin)located adjacent to a surface of the primary or secondary magneticstructure where magnetic flux density may exceed a particular value(e.g., 0.5 mT).

Metal detection has many applications in various industrial, militaryand security-related areas. Metal detectors are used e.g., for de-mining(detection of land mines), the detection of weapons such as knives andguns e.g., in airport security, geophysical prospecting, archaeology,and treasure hunting. Metal detectors are also used to detect foreignobjects in food, and in the construction industry to detect steelreinforcing bars in concrete and pipes and wires buried in walls andfloors.

In many applications, metal detectors achieve the required highsensitivity by frequently recalibrating their sensors and circuits. Inthese applications, presence of metal objects may be excluded during aprocess of recalibration based on user input. In contrast, high powerinduction charging application may have to operate largelyautomatically, autonomously and unattended by humans. As such, certainaspects of various embodiments are directed to object detection systemsconfigured to provide inherent detection sensitivity and stability overyears without the need for substantial recalibration.

Passive optical sensing (described in Conductix-Wampfler,Abschlussbericht zum Verbundvorhaben “Kabelloses Laden vonElektrofahrzeugen”, im Rahmen des FuE-Programms “Förderung von Forschungand Entwicklung im Bereich der Elektromobilität”, Weil am Rhein, Oktober2011) (hereinafter “Conductix-Wampfler”) using a camera sensitive invisible light and/or in shortwave infrared may be used to detect foreignobjects in a predetermined area. Since ‘metal objects’ in general do nothave peculiar characteristics in this wavelength range, this method maynot provide sufficient selectivity, so that any foreign object will bedetected including those that do not represent a hazard. This may beundesirable for users of the system in some cases. Moreover, opticalsensors may not be particularly suitable in the harsh environment asexpected beneath a vehicle, where there is normally strong pollution andrisk of damage from mechanical impacts. Special protective measures suchas automatic cleaning, etc. may be needed.

Active optical sensing of foreign objects by emitting light signals inthe visible or short wave IR range may be provided. This technique isused in conjunction with 3D cameras based on time-of-flight rangingtechniques described in Ringbeck, T, Hagebeuker, B. “A 3D time of flightcamera for object detection”, Optical 3-D Measurement Techniques, ETHZürich, Plenary Session 1: Range Imaging I, 09-12 Jul. 2007 (hereinafter“Rinkbeck”). In some cases, using active optical sensing may not be ableto resolve a small and thin object (e.g., a coin) sitting on the surfaceof an energy transfer pad. Furthermore, as with passive optical sensing,the method may not be able to distinguish metal objects from non-metalobjects. Any object that appears opaque at optical wavelengths may bedetected.

Since hazardous objects are those objects that have the potential forheating up to critical temperatures, thermal sensing described inConductix-Wampfler is another approach ignoring environmental factors.One solution may be achieved by integrating temperature sensors into theenclosure of the energy transfer pads. To localize small hot objects, ahigh sensor density may be provided e.g., with a raster size of 30 mm.Since sensors need to be mechanically protected, they may be embedded into the plastic enclosure at sufficient depth, which may decrease theirsensitivity and increase their detection latency due to the heatpropagation delay. Such approach may be slow and unreliable in regardsto detecting objects with high risk of inflammation e.g., a thinmetalized paper foil.

The use of pyro-electric passive infrared (PIR) sensors described inConductix-Wampfler and described in WO 2011/006876 A2 (Wechlin M.,Green, A. (Conductix-Wampfler AG), ‘Device for the inductive transfer ofelectric energy’) may provide an alternative thermal sensing solution.These sensors that are normally used for detecting persons by theirmotion are sensitive in the long-wave IR range where radiation spectraldensity becomes maximal for objects at temperatures below 100° C.(Wien's law). As the result of a trade-off between number of sensors perunit area and costs, a PIR sensor array may not provide adequate spatialresolution for detecting objects as small as 20 mm on a larger area suchas an electric vehicle inductive charging pad. This may be particularlytrue if the temperature difference between a foreign object and the padsurface becomes low e.g., in case of pad heating by sun irradiation thatmay have happened before vehicle was parked for charging. Apart from thelimited sensitivity, this solution may be vulnerable to pollution andmechanical impacts.

IR cameras described in Conductix-Wampfler based on bolometer focalarrays may provide sufficient resolution in the optimum wavelengthrange. However, they may be costly. This may be particularly true forrugged designs e.g., suitable for installation beneath a vehicle. Suchcameras may require special protective measures such as a mechanicalshutter that are closed if thermal detection is not used and the vehicleis on the move. Additionally, automatic cleaning of the IR lensprotecting window using little wipers or similar concepts may berequired. In addition, a vehicle bottom mounted camera may have anunfavorable angle of view for monitoring the entire critical space andthe limited space for mounting the camera if a minimum ground clearancehas to be respected. Customized ultra wide angle IR lenses may be neededif the camera is mounted close to the magnetic structures or highresolution (high number of pixels) if the camera is mounted in somedistance where the scenery appears highly perspective and not wellmatched to a commercial-off-the-shelf bolometer array.

Acoustic sensing described in Conductix-Wampfler may be an alternativeapproach for detecting foreign objects. Acoustic sensing may beperformed actively using radar principles by emitting ultrasonic signalsand analyzing the received response. Ultrasonic frequencies e.g., above200 kHz may provide sufficient resolution for detecting presence of asmall and thin object e.g., a coin sitting on the surface of an energytransfer pad. However, all objects of a certain mass density may bedetected thus prone to false alarms.

As opposed to ultrasonic radar, passive acoustic sensing described inConductix-Wampfler has the potential for selectively detecting metalobjects. When exposed to strong magnetic fields, electrically conductiveobjects begin to vibrate due to forces occurring between moving charges(currents) of the magnetic structure and of the foreign object (eddycurrents). These forces can be explained by Lenz's law and Lorentzforces. These forces alternate at the first harmonic (double frequency)of the alternating magnetic field. For magnetic field frequencies above20 kHz, these acoustic emissions may be above 40 kHz in the ultra-sonicrange. Therefore, metal objects may be detected by their acousticemissions at double frequency or even at harmonics thereof. Since theentire magnetic structure is vibrating at that frequency, high spatialresolution may be provided in order to detect presence of small objects.This may be achieved at ultrasonic frequencies using phased arraytechnology requiring a high number of transducers. Because of inductionheating and unacceptable eddy current losses, it may be difficult, insome cases, to integrate sensors into the pad's surface. Sensors mayhave to be arranged e.g., along the periphery of the vehicle pad assuggested in Conductix-Wampfler, a solution likely not providingsufficient resolution for reliably detecting small objects. As with theoptical and IR sensors, ultrasonic transducers may be prone to pollutionand damage from mechanical impacts.

Capacitive sensing described in Conductix-Wampfler is an approach basedon electric field sensing. Capacitive sensing is used in touch screens.A capacitive sensor array may be accomplished e.g., using a thin openloop wire structure generating leakage electric fields. This wirestructure may be embedded into the pad's plastic enclosure. As withoptical sensing, capacitive sensing cannot provide selective detectionof metals. Capacitive sensing may sense any object that changes anelectric field thus a capacitance. This includes conductive materialsand non-conductive dielectric materials e.g., little stones, wet leaves,etc.

In accordance with certain embodiments, inductive sensing based onmagnetic fields may be preferably used since objects that can be sensedvia the magnetic field may be objects that are potentially hazardous.Magnetic field sensing may be highly selective on electricallyconductive and ferromagnetic objects. At frequencies e.g., below 20 MHzwhere a magnetic field may be considered quasi-stationary, there may bevirtually no interaction with non-conductive dielectric objects andalmost no interaction with badly conducting materials such as water withhigh salinity, or water-drenched paper, wet wood and foliage, etc.

In some cases, it may be somewhat difficult to detect small objects dueto limited range. Smaller objects may be detected, in some cases, ifthey are in close proximity to a sensor. There may be locations in thespace in which objects need to be detected, where smaller objects cannotbe detected. This is particularly true if for reasons of mechanicalprotection and robustness, magnetic field sensors are integrated intothe enclosure of an energy transfer pad.

WO 2011/006758A2 (Wechlin, M., Green, A. (Conductix-Wampfler AG),‘Device for the inductive transfer of electric energy’) (hereinafter“Wechlin”) discloses a device for detecting presence of metal objectthat is located within a predetermined space between a primary andsecondary inductance. This has at least one unit for measuringinductance, a measuring unit for measuring the impedance of themeasuring inductance and an evaluation unit that is connected to themeasuring unit.

According to Wechlin, measuring inductance can be similar to the primaryinductance, and the primary inductance is used for detecting a metalobject. This may be applicable to solutions requiring less detectionsensitivity e.g., for larger objects. To increase detection sensitivitye.g., for objects significantly smaller than the primary structure, thesize of the measuring inductance may be reduced.

The sensing device of Wechlin may be equipped with a plurality ofsmaller measuring inductances, which form a regular two-dimensionalarrangement extending approximately in one plane. The plane liesperpendicular to the main direction of the magnetic field that isgenerated by the primary inductance during operation. In regards to alower cost and easier production, these measuring inductances may beplanar coils on a common substrate (e.g., a multilayer PCB). Forachieving an increased coil packaging density (coils overlapping),Wechlin describes integration of a second coil array with an equalraster size but offset relative to the first array by one half of theraster size.

Wechlin also describes that measuring inductances are connected togetherforming groups and there is an impedance measuring unit per group. Inanother embodiment, Wechlin describes a common impedance measuring unitfor the entire array. In this embodiment, the impedance measuring unitmay be connected to single measuring inductances or groups of measuringinductances via an analog multiplexer (switch).

The evaluation unit as described in Wechlin compares measured impedancevalues with pre-stored reference values and provides outputs to indicatea deviation exceeding predetermined values. These outputs may beconnected to a control unit and an indicator device to output an opticalor acoustic alert signal. The control unit may also output a command todeactivate inductive energy transfer.

In Conductix-Wampfler, an alternative method for detecting electricallyconductive or magnetizable objects is described. This method uses anumber of measuring coils placed on top of the primary structure. Inthis method, detecting of metal objects or ferromagnetic objects isbased on their effect of altering or perturbing the magnetic field aspresent at the surface of the primary structure. Conductix-Wampfler,describes measuring the voltage that is induced into each of the coilsat inductive power transmission frequency. Conductix-Wamplfer alsoindicates that this method is sensitive to displacement in x and ylikely but not explicitly referring to the displacement (alignmentoffset) of the secondary vs. the primary structure.

Conductix-Wampfler also describes another method called ‘trafo’. The‘trafo’ method uses capacitively loaded coils tuned to a frequency near1 MHz forming a resonant transformer. Metal objects placed on thetransformer coils change the field and thus the transmitted power.

FIG. 8A is a diagram of a portion of exemplary object detectioncircuitry configured to detect an object 824 a via measuring the voltageinduced into a sense loop 822 a, in accordance with an embodiment. Inaccordance with various embodiments, the sense loop 822 a may be amulti-turn loop (coil) e.g., for increasing sensitivity. Eddy currentsin a metal object 824 a placed in the proximity of the loop change themagnetic flux through the loop and thus the induced voltage. Themagnetic field B_(ex) is an external field that is generated forinductive energy transfer at an operating frequency. For example, thebase system induction coil 104 a may generate the magnetic field B_(ex).The sense loop induced voltage in general changes in both amplitude andphase depending on the electric and magnetic properties of the object.

FIG. 8B is another diagram of a portion of exemplary object detectioncircuitry configured to detect an object 824 b via measuring a senseloop impedance, in accordance with an embodiment. In general, a senseloop 822 b may be a multi-turn loop (coil). To measure the loopimpedance, a small high frequency sense current I_(sense) is injectedinto the sense loop 822 b. The metal object 824 b in proximity of theloop modifies the magnetic flux as generated by the sense loop currentI_(sense) and thus modifies the loop's inductance and resistance(imaginary and real part of the impedance).

A frequency differing from the external magnetic field (e.g., anothermagnetic field provided for wireless energy transfer) may be used forimpedance measurements in order to avoid interference from thefundamental or harmonics of the external magnetic field.

FIG. 8C is yet another diagram of a portion of exemplary objectdetection circuitry configured to detect an object 824 c via measuringthe coupling or the mutual impedance (mutual inductance) between aprimary and a secondary sense loop structure 822 c and 822 d, inaccordance with an embodiment. In general, the sense loops 822 c and 822d may be multi-turn loops (coils). A change in mutual inductance ormutual impedance may be sensed by injecting a small high frequencycurrent into the primary loop 822 c and measuring the open circuitvoltage at the secondary loop (amplitude and phase). Alternatively, thesecondary loop may be resistively loaded and energy transfer into theload is measured. Here, the metal object modifies the magnetic flux thatis generated by the primary loop current I_(sense) and that is passingthrough the secondary loop, thus the mutual impedance that has animaginary and a real part in general.

The mutual impedance method may also be understood as the loop inducedvoltage method however with the difference that the external magneticfield (e.g., as used for wireless power transfer) is supplanted by amagnetic field that is generated particularly for the purposes of metaldetection by a dedicated primary sense loop 822 c at a frequencydiffering from the frequency of the external magnetic field as usede.g., for energy transfer. The primary loop may cover the entire area ora substantial portion of the area to be protected.

Inductive Sensing

In accordance with certain aspects of certain embodiments, inductivesensing or magnetic field sensing may provide several benefits, forexample:

-   -   Inductive sensing may be highly selective on well conducting        (metallic) objects    -   No impairments by other non-metallic (dielectric) objects are        expected;    -   Inductive sensing circuitry may be integrated into the plastic        enclosure of an energy transfer pad to protect sensors from        environmental impacts (pollution, mechanical) with minor        performance degradation; and    -   Inductive sensing circuitry may be incorporated into the        charging base since in most cases objects may be laying on the        base pad surface. This may allow for cost savings in the vehicle        onboard equipment.        Methods and Concepts to Enhance Inductive Sensing

As stated above, large loops may not provide sufficiently highsensitivity as needed for detecting a coin, a key, or a lid of abeverage can, which may be significantly smaller than the area to beprotected. In accordance with various embodiment, for detecting smallobjects, a plurality of smaller loops may be used according to variousembodiments.

FIG. 9 is a side view of a sense loop 922 embedded within a wirelesscharging pad 926, the sense loop 922 configured to detect an object 924,in accordance with an exemplary embodiment. The pad has a plasticenclosure 928 and may be configured to hold a planar sense loop 922 anddetect an object placed anywhere on the surface of the pad 926. Thecharging pad 926 may further include a base system induction coil 104 a(FIG. 1) and associated circuitry as described above with reference toFIGS. 1-3 and may be configured to detect an object on the pad 926.Further examples of pad configurations are shown in FIGS. 5A-5D.

The innate sensitivity of a sensor may be defined as the percentagechange of the measured quantity (e.g., loop induced voltage, loopimpedance) as caused by the presence of the smallest object (referenceobject) if placed at a worst case position. The overall sensitivity of aforeign object detector depends on the innate sensitivity of the sensorand on the performance of additional post processing methods that may bepart e.g., of the evaluation unit.

For objects smaller than the loop size, the innate sensitivity increaseswith decreasing loop size. Decreasing loop size implies increasing thenumber of loops required to cover a given area resulting in increasedcomplexity and costs and higher probability of false alarm and failure.

In accordance with certain embodiments, an adequate trade-off betweeninnate sensitivity and circuit complexity may be achieved with a loopraster size of equal or double the size of the smallest object to bedetected. For example, if the smallest object is a coin of 20 mmdiameter, an adequate loop raster size may be 30 mm. This may be forboth the loop induced voltage method and the loop impedance method.

FIG. 10 is a diagram of a portion of exemplary object detectioncircuitry for detecting an object 1024 located at different positionsrelative to a sense loop 1022, in accordance with an exemplaryembodiment. As an example, FIG. 10 may illustrate changes of loopinduced voltage at 40 kHz in percent using a coin 1024 (e.g., ofdiameter 25 mm and thickness 1.7 mm) placed at different positions on arectangular wire loop 1022. The loop may be made of 3 turns of thinenamel copper wire. The coin may be placed at a height above the loopstructure in regards to a possible future integration of the loop arrayinto a plastic enclosure 928 of a magnetic pad 926 as shown in FIG. 9.For example, when the object 1024 is placed in the upper left corner ofthe sense loop 1022, a change in percent of loop induced voltage may beon the order of, for example, negative six percent. When the object 1024is placed in the center of the sense loop 1022, a change in percent ofloop induced voltage may be on the order of, for example, negativetwenty-two percent. When the object 1024 is placed towards the upperright corner of the sense loop 1022, a change in percent of loop inducedvoltage may be on the order of for example, negative fifteen percent.These values are provided to illustrate relative degrees of changes inpercent of loop induced voltage when an object 1024 is located indifferent positions and are merely exemplary.

Likewise, changes in loop impedance may also be provided for differentpositions for the configuration shown in FIG. 10. For the object 1024,measured impedance changes are changes due substantially to its changinginductance. For example, when the object 1024 is placed in the upperleft corner of the sense loop 1022, a change in percent of loopimpedance may be on the order of, for example, negative two percent.When the object 1024 is placed in the center of the sense loop 1022, achange in percent of loop impedance may be on the order of, for example,negative eight percent. When the object 1024 is placed towards the upperright corner of the sense loop 1022, a change in percent of loopimpedance may be on the order of for example, negative five percent.These values are provided to illustrate relative degrees of changes inpercent of impedance when an object 1024 is located in differentpositions and are merely exemplary.

Though showing higher innate sensitivity, the induction loop method mayneed to cope with significant changes of the magnetic field as caused bythe varying position (offset and distance) of the adjacent magnetic pad,the vehicle's underbody structure or a conductive ground. These effectsmay need to be taken into account.

On the other hand, the loop impedance method exhibits lower innatesensitivity, but may also be less sensitive on changes in its metallicand ferromagnetic environment. As opposed to the induction loop method,its sensitivity may slightly degrade if measured via the connectinglead. Depending on the size of the loop array and the location of theimpedance analyzer, a possible worst-case lead length may be 1 m,assuming the impedance analyzer is integrated into the magnetic pad 926.

For both methods, the object 924 may have the strongest impact if placedin the center of the loop 922 and weakest impact if placed on an edgeand particularly in the corner. It shall be noticed however that for‘edge’ and ‘corner’ position, impedance/induced voltage may also changein adjacent loops, assuming an array of loops. Simultaneous changes inadjacent loops can be exploited in post processing to improve overalldetection sensitivity in accordance with various embodiments.

Shape, Orientation and Packing of Sense Loops

FIGS. 11A, 11B, and 11C are diagrams of different exemplaryconfigurations for sense loops configured to detect an object, inaccordance with exemplary embodiments. Using an array 1122 ofoverlapping loops 1122 a and 1122 b as illustrated in, for example asshown in FIG. 11A, may improve innate sensitivity of an inductive sensorsystem. In this arrangement, loops 1122 a and 1122 b are somewhat largerthan the raster size of the array. Overlapping the loops as shown inFIG. 11A improves worst case sensitivity at the expense of the best casesensitivity (coin centered in the loop). Overlapping reduces thesensitivity ripple on a sense loop array 1122. For an embodiment using aprinted circuit board, overlapping in rows and columns may use, forexample, at least 4 copper layers.

Innate sensitivity variations may be equalized by dimensioning the loopsslightly larger than the raster size equally in both x and y direction.A ratio of overlapping area to non-overlapping area may be in the rangefrom 0.5 to 2 that may provide various benefits.

Instead of using a square or a rectangular shape, loops 1122 a and 1122b may be circular-, hexagonal-, triangular-shaped in accordance withvarious embodiments. In a loop array 1122, densely packed hexagonalloops may provide improved sensitivity with a non-overlapping structurerequiring a lower number of copper layers when implemented in a printedcircuit board.

Moreover, the loop's size, shape or raster size may be adapted to localsensitivity requirements. On a surface with local variations of themagnetic flux density e.g., there may exist areas/zones with lowerpotential for thermal effects thus relaxed sensitivity requirements.Larger loops may be placed in these less critical areas, trading-offsensitivity, wiring and circuit complexity.

For the loop impedance measuring method, other loop topologies such asdouble loops as shown in FIG. 11B, triple loops (clover leave), or evenquadruple loops, producing a magnetic flux arch from one pole area toanother pole area when driven by a sense current. FIG. 11B shows atopology for a double loop 1122 c showing sense current directions.These structures may be used for an optimized detection performancee.g., in applications where a predominant horizontal field component wasuseful for detecting metal objects.

Combinations of structures generating differently oriented magneticfields (e.g., double loop plus single loop) generates a rotatingmagnetic vector field if driven with 90° phase offset. The use of suchcircular or elliptically polarized fields may also lead to improveddetection performance in certain applications.

In accordance with an embodiment, innate sensitivity of the loop inducedvoltage method may be considerably increased by using wire loops 922 ina plane that is substantially parallel to the magnetic field lines suchthat there is virtually zero flux passing through the loops. For itsintegration into the enclosure of a charging pad 926, low profilesolenoid coils 1122 as illustrated in FIG. 11C where the solenoid coils1122 may be in a plane substantially parallel to the direction of themagnetic field.

Even a small metal object may dramatically raise the flux through theloop as it changes the direction of the magnetic field lines. The phaseof the loop induced voltage in this case generally is offset relative tothe external magnetic field. As already stated above, this phase offsetdepends on the electric and magnetic properties of the object. Aconductive object produces a different phase shift than a ferromagneticobject.

An increased flux and a phase shift may however also be experienced ifmagnetic pads are displaced or pad currents change. Resonant inductiveenergy transfer is characterized by a 90 degrees phase shift betweenprimary and secondary current. This may also cause a phase shift in thesensed voltage.

In accordance with some embodiments, using an orthogonal loop system(loops substantially in perpendicular planes e.g., a planar coil and asolenoid) may also enhance sensitivity of the loop induced voltagemethod. Since metal objects may generally change the direction of themagnetic field in their surroundings, sensing flux components by anorthogonal loop arrangement may provide additional information toimprove the detector's performance.

Moreover, the induction balance using a pair of loops e.g., in a double‘D’ arrangement is a technique implemented in metal detectors e.g., asused for detection of mines. Balance is maintained by continuouslyrunning a calibration process. A foreign object may slightly change theflux passing through the two coils. This change in general may beunequal in the two loops thus temporarily unbalancing the bridge. Thismethod may be sensitive to situations where the magnetic field may bechanging due to other factors.

An inductive balance may be also accomplished based on the loopimpedance of FIG. 8A or the mutual impedance method using two coupledloops of FIG. 8C. For the latter, loops 822 c and 822 d may bepositioned in a manner such that flux generated by the primary loop 822c virtually or substantially cancels out in the secondary loop 822 d(zero coupling). When an object is placed in the sensitive area of theseloops 822 c and 822 d, it unbalances flux through the secondary thusdramatically increasing coupling. The pad's magnetic structure may alsounbalance the system. Even if these effects were taken into account inthe printed circuit board layout, the solution may be extremelysensitive on fabrication tolerances.

To avoid excessive heating and consecutive damage of the PWB in theunlikely event of a short circuit in a sense loop, the loops may befused. A fuse may be accomplished by design using thin wire or thin PWBtraces or if electric resistance increase is not permissible byinserting a diminution in the PWB traces at defined locations.

A Method for Enhancing the Magnetic Field Sensing

FIG. 12 is a functional block diagram of an exemplary circuit 1200configured to detect an object based on magnetic field sensing, inaccordance with exemplary embodiments. This section describes anembodiment for enhancing performance of a metal object detector that isbased on sensing a magnetic field (flux density) as generated by amagnetic structure e.g., a charging pad 926 over a predetermined area.The charging pad 926 may correspond to a charging system as describedabove with reference to FIGS. 1-3. The circuit 1200 may include severalsense loops 1222 a, 1222 b, 1222 c, and 1222 d (referred to herein aftercollectively as sense loops 1222). The sense loops 1222 may form a partof an array of densely packed loops that cover an area to be protectedin which metal objects may be detected. As described above, detecting anobject 924 may be accomplished by measuring the voltage induced into thesense loops 1222. The circuit 1200 includes a detection circuit 1230that selectively couples to each of the sense loops 1222 via amultiplexer 1228. The detection circuit 1230 includes a magnetic fieldmeasuring unit 1234 configured to measure a magnetic field strength ofeach of the sense loops 1222. A measured value of the sense loop B_(k)is provided to an evaluation unit 1232 including a comparator 1236 and adecider 1238. The comparator receives the measured magnetic field valueB_(k) and compares the value B_(k) with a reference magnetic field valueB_(ref,k). The reference magnetic field value may correspond to anexpected value of the magnetic field for a sense loop 1222 a in theabsence of any object to be detected. Based on the output of thecomparator 1236, the decider 1238 is configured to determine whether anobject is present. For example, the decider 1238 may determine that thedifference between the measured value B_(k) and the reference value isgreater than a threshold and output a signal that an object is detectedin response. The decider 1238 may further compensate the output of thecomparator based on known operating characteristics that may impact theresult to increase.

Alternatively, with respect to the circuit in FIG. 12, an array of Halleffect sensors or sensors may be used that are based on the GiantMagnetic Resistance (GMR) effect or any other method suitable to sense amagnetic field.

It may be also useful to sense at least one of an x-component,y-component, and z-component of the magnetic field vector separately.

Embodiments according to the circuit of FIG. 12 may be useful in usecases where there is a magnetic field on the base pad surface that issubject to temporal changes (perturbations, distortions) e.g., due tothe presence of the vehicle pick-up pad and the vehicle's metallicunderbody structure that may be at different vertical and horizontalpositions (different alignment offsets). Evaluation may be based on aleast mean square error criterion and may be implemented into thedetector's evaluation unit 1232. Other more sophisticated methods usingother error metrics and iterative processes e.g., RANSAC (Random SampleConsensus method) may also be used.

An exemplary process for detecting an object may be formulated asfollows:

Find a small metal object that excerpts a little impact (distortion,perturbation, disturbance) on the magnetic field pattern as present on amagnetic charging pad's surface. This field pattern may exhibit strongvariations in flux density due to an inhomogeneous magnetic structure(coil, ferrites) and additionally temporary variations (distortions) dueto the different positions of the vehicle pad and the vehicle's metallicunderbody structure. For example, there may be significant fielddistortion and other impact from pad alignment offset.

However, the impact on the magnetic field on a surface of a pad 936exerted by a small metal object (e.g., a coin particularly if placed inthe order of four adjacent loops where innate sensitivity per loop islower) may be small in comparison to field distortions due to alignmentoffsets. In such as case, an impact on a magnetic flux density patternmay be small.

The impact of the object 924 however may be made visible by subtractingthe field pattern as measured in absence of the object 924 (thereference field pattern) from the field pattern measured in presence ofthe object.

In some cases, it may be difficult if the object 924 has to be detectedin a magnetic field pattern that is distorted relative to the referencepattern. The reference pattern may be taken and stored in the system aspart of a calibration procedure in zero offset conditions and at adefined air gap distance. The object however may have to be detected indifferent conditions as resulting in realistic use cases. The method ofcomputing the differential field patter may not be sufficient in somecases due to errors due to the field distortion in offset conditions maybe far greater than the impact of the object requiring a moresophisticated methods.

As such, in accordance with an embodiment, an improved detection methodmay be based on a least mean square approach as follows:

DEFINITIONS

-   B_(ref) (x_(i),y_(j)): Reference flux density values (reference    field pattern extending in x- and y-direction) e.g., as stored in    foreign object detection system and obtained by calibration in    predetermined conditions at production in factory-   {tilde over (B)}(x_(i),y_(j)): Actual flux density values (distorted    field pattern) as measured in a realistic scenario e.g., in presence    of offsets and different air gap distance-   γ(x_(i),y_(j); a₁, a₂, . . . , a_(L)): a correction function with    multiple parameters compensating for the distortion effect in the    actual field pattern. In the simplest case, this function may be a    plane whose z-offset and x- and y-slope can be modified by    parameters a₁, a₂, a₃.

The method may include computing mean square error in differential fieldvalues as resulting after applying correction function to the actuallymeasured field values and subtracting the reference flux density values

${\overset{\_}{\varepsilon^{2}}\left( {a_{1},a_{2},\mspace{11mu}\ldots\mspace{14mu},a_{L}} \right)} = {\sum\limits_{i = 0}^{N}\;{\sum\limits_{j = 0}^{M}\;\left\lbrack {{{\overset{\sim}{B}\left( {x_{i},y_{j}} \right)}{\gamma\left( {x_{i},{y_{j};a_{1}},a_{2},\mspace{11mu}\ldots\mspace{14mu},a_{L}} \right)}} - {B_{ref}\left( {x_{i},y_{j}} \right)}} \right\rbrack^{2}}}$

In addition, a method may include determining optimum values forparameter set a₁, a₂, a_(L), minimizing the mean square error

$a_{1{\_ opt}},a_{2{\_ opt}},\mspace{11mu}\ldots\mspace{14mu},{a_{L\_ opt}->{\min\limits_{a_{1},a_{2},\mspace{11mu}\ldots\mspace{14mu},a_{L}}\overset{\_}{\varepsilon^{2}}}}$

The method further includes applying a correction function with optimumparameters to measured field pattern and perform object detection on theresulting LMS differential patternΔB(x _(i) ,y _(j))={tilde over (B)}(x _(i) ,y _(j))γ(x _(i) ,y _(j) ; a₁ _(_) _(opt) ,a ₂ _(_) _(opt) , . . . ,a _(L) _(_) _(opt))−B _(ref)(x_(i) ,y _(j))

The following decision rule may apply:

-   -   Hypothesis ‘Object present’, if at least one differential flux        density value exceeds a predefined threshold.    -   Hypothesis: ‘No object’, else.

This method may be significantly improved by using a set of referencepatterns instead of a single reference pattern B_(ref) (x_(i),y_(j)).These reference patterns may have been obtained in different offset andair gap conditions as part of a calibration procedure performed atfactory. The reference pattern that results in the least mean squareerror is chosen to compute the differential field pattern.

The least mean square method may not perform in the expected way inpresence of a large metal object. Since such large objects may easily berecognized, the leas mean square method may be conditionally used oradapted accordingly.

Alternative Concepts for Enhancing the Loop Impedance Sensing Method

Several methods and embodiments are further described herein thatimprove performance and/or reduce wiring and circuit complexity of aloop impedance based metal object detector. These are in particular:

-   -   Using an array of resonant loops and measuring their resonant        frequency to sense a metal object    -   Using weakly coupled resonant loops e.g., using either inductive        or capacitive coupling.    -   Using canonical structures of inductively or capacitively        coupled resonant loops forming a coupled resonator filter acting        as a signal propagation medium        Resonant Loops and Measuring their Resonant Frequency

FIG. 13 is a functional block diagram of an exemplary circuit 1300configured to detect an object based on sense loop impedancemeasurements, in accordance with exemplary embodiments. The circuit 1300may include several sense loops 1322 a, 1322 b, 1322 c, and 1322 d(referred to herein after collectively as sense loops 1322). The senseloops 1322 may form a part of an array of densely packed wire loops thatcover an area to be protected in which metal objects may be detected.The circuit 1300 includes a detection circuit 1330 that selectivelycouples to each of the sense loops 1322 via a multiplexer 1328. Thedetection circuit 1330 includes an impedance measuring unit 1334.Impedance Z_(k) at the multiplexer port is measured for each loop 1322selected by the multiplexer 1328 sequentially and periodically via theimpedance measuring unit 1334. A measured value of the sense loop B_(k)is provided to an evaluation unit 1332 including a comparator 1336 and adecider 1338. An object 924 is detected based on the differentialimpedance as resulting by subtracting a reference impedance valueZ_(ref,k) from the measured impedance value Z^_(k) for k=1 . . . N asshown by the comparator 1336. A decider unit 1338 receives input fromthe comparator 1336 and determines whether an object is detected. Forexample, if the difference between a measured value and the referencevalue exceeds a threshold and may incorporate any of the functionalityas described above, for example, with reference to the least mean squaremethod.

FIG. 14A is a functional block diagram of an exemplary circuit 1400Aconfigured to detect an object 924 based on sense loop resonantfrequency measurements, in accordance with an embodiment. The circuit1400A may be configured to detect an object 924 based on measuring aloop impedance to determine a resonant frequency. The circuit 1400Aincludes sense loops 1422A-a and 1422A-b. The sense loops may have aninductance L. As used herein, a sense loop 1422A-a may be referred to asor be configured as a sense circuit. The sense loops 1422A-a and 1422A-bare coupled to a detection circuit 1430A via a coupling circuit 1426A.Some combination of the coupling circuit 1426A and the sense loops1422A-a and 1422A-b form resonant circuits. For example, in anembodiment, the sense loops 1422A-a and 1422A-b include reactivecomponents (e.g., a capacitor) to form resonant circuits configured toresonate at a particular frequency. In another embodiment, the couplingcircuit 1426A includes reactive components electrically coupled to eachof the sense loops 1422A-a and 1422A-b to form resonant circuitsconfigured to resonate at a particular frequency. Either series orparallel tuning may be used. Exemplary embodiments for configuration ofthe resonant circuits are described below. In some embodiments, thefrequencies of the resonant circuits formed at least by each sense loop1422A-a and 1422A-b may be the same while in some embodiments they maybe different. The coupling circuit 1426A may include a multiplexer toselectively couple each of the sense loops 1422A-a and 1422A-b to thedetection circuit 1430A. The coupling circuit 1426 is configured toreduce a variation of the resonant frequencies of the sense loops1422A-a and 1422A-b by the detection circuit 1430A in the absence of anobject.

The detection circuit 1426A is configured to detect objects based on thechange of the resonant frequency of each sense loop 1422 a and 1422 brelative to a reference/calibration value e.g., stored in a look uptable as part of the system. For example, the detection circuit 1426Amay be configured to measure first and second characteristics thatdepend on the first and second resonant frequencies of the sense loops1422A-a and 1422A-b, respectively. The detection circuit 1426A isconfigured to detect presence of an object in response to detecting adifference between the first measured characteristic and a correspondingcharacteristic that depends on the first resonant frequency or adifference between the second characteristic and a correspondingcharacteristics that depends on the second resonant frequency. Thecharacteristic may be a measured resonant frequency, a quality factor,or other characteristic from which a frequency at which a sense loop1422A-a is resonating is determined. Furthermore, the use of multiplesense loops 1422A-a and 1422A-b may allow for the detection circuit todetect a position of the object 924 relative to at least one of thesense loops 1422A-a and 1422A-b. The sense loops 1422A-a and 1422A-b maybe a part of an array of densely packed sense loops arranged in a planarform to cover an area, for example of a wireless charging pad 936 to beprotected. Each of the sense loops including sense loops 1422A-a and1422A-b may be selectively coupled to the detection circuit 1430A andallow for determining position information of an object 924 to bedetected in a pre-determined space.

FIG. 14B is a functional block diagram of an exemplary circuit 1400Bconfigured to detect an object 924 based on sense loop resonantfrequency measurements, in accordance with an embodiment. The circuit1400B includes sense loops 1422B-a and 1422B-b. The sense loops may havean inductance L. As compared to FIG. 14A, the sense loops 1422B-a and1422B-b include reactive components such as capacitors C1 and C2 suchthat each sense loop 1422B-a and 1422B-b forms a resonant circuit.Either series or parallel tuning may be used. The sense loops 1422B-aand 1422B-b are coupled to a detection circuit 1430B via a couplingcircuit 1426B. The coupling circuit 1426B may not form a part of aresonant circuit in accordance with the embodiment shown in FIG. 14B. Insome embodiments, the frequencies of the resonant circuits formed atleast by each sense loop 1422B-a and 1422B-b may be the same while insome embodiments they may be different. The coupling circuit 1426B isconfigured to reduce a variation of the resonant frequencies of thesense loops 1422B-a and 1422B-b by the detection circuit 1430B in theabsence of an object. The detection circuit 1430B may function similarlyas the detection circuit 1430A of FIG. 14A.

To measure the loop impedance and particularly the resonant frequency, afrequency significantly higher than that of the alternating magneticfield used for wirelessly transferring power, preferably in theMegahertz range may be used. The sense frequency however may not be toohigh e.g., <20 MHz if sensitivity on dielectric objects has to be keptlow.

FIG. 15 is another functional block diagram of an exemplary circuit 1500configured to detect an object 924 based on sense loop resonantfrequency measurements, in accordance with an exemplary embodiment. Thecircuit includes sense loops 1522 a, 1522 b, 1522 c and 1522 d(hereinafter referred to collectively as sense loops 1522) that may bepart of an array of sense loops. In some embodiments, the sense loops1522 may substantially be configured to define a common plane over apredetermined area to be protected. The sense loops 1522 are coupled toa detection circuit 1530 via a multiplexer 1528 configured toselectively couple each of the sense loops 1522 to the detection circuit1530 including a resonant frequency measuring unit 1534 and anevaluation unit 1532. The resonant frequency measuring unit 1534includes a capacitor C such that a sense loop 1522 a coupled to theresonant frequency measuring unit 1534 forms a resonant circuitconfigured to resonant a particular resonant frequency. It is noted thatwith reference to FIG. 14A, a coupling circuit 1426A may include themultiplexer 1528 and the resonant frequency measuring unit 1534including capacitor C shared by all sense loops 1522 to form eachresonant circuit. The resonant frequency measuring unit 1534 includes anoscillator 1546 configured to drive a coupled sense loop 1522 a over arange of frequencies to cause the sense loop 1522 a to resonate at aparticular frequency. The resonant frequency measuring unit 1534 furtherincludes a phase comparator 1548 configured to detect a phase between ameasured voltage and current (e.g., a zero-crossing of a phasefunction). In addition, a gain/filter 1550 may also be included.

The output of the resonant frequency measuring unit 1534 may correspondto a measured resonant frequency of a sense loop 1522 a that is providedto an evaluation unit 1532 of the detection circuit 1530. The evaluationunit 1532 includes a comparator 1536 configured to compare the receivedmeasured resonant frequency value for a sense loop 1522 a with areference frequency value. The output of the comparator 1536 is providedto a decider 1538 configured to determine, based at least in part on adifference between the measured and reference value if an object 924 isdetected. Combining information from multiple loops 1522 may allow fordetermining position information regarding an object 924 to be detected.In addition, as is further described below, the evaluation unit 1532 mayreceive sense temperature inputs to compensate for operating conditionsthat may impact the measured resonant frequency due to conditions otherthan foreign objects.

In some aspects, the resonant loop method as described with reference toFIGS. 14 and 15 and further below (e.g., FIG. 16) may provide variousbenefits, at least including:

-   -   Measuring a resonant frequency may be simpler and more accurate        than measuring an impedance or inductance. A detection circuit        1430 or 1530 may have less components and in some aspects        limited to using an oscillator and a phase comparator detecting        the phase between measured voltage and current e.g., the        zero-crossing of the phase function.    -   The capacitor may be also already provided to suppress voltage        induced by the strong alternating magnetic field used for        wireless power transfer as present on the pad's surface and        harmonics noise thereof. As such adding the capacitor does not        add extra complexity. The resonance may act as a sense signal        pre-conditioning (noise reduction) filter that also moves        accordingly if a loop 1522 a is detuned by a metal object.    -   Any temperature drift or aging of the capacitor may have a        common effect on all resonant frequencies thus can be easily        estimated and corrected in the evaluation unit (see section        below).

FIG. 16 is yet another functional block diagram of an exemplary circuit1600 configured to detect an object based on sense loop resonantfrequency measurements, in accordance with an exemplary embodiment. Eachof the sense loops 1622 a, 1622 b, 1622 c, and 1622 d is electricallycoupled to a resonance capacitor C₁, C₂, C_(k), and C_(N). It is notedthat with reference to FIG. 14A, a coupling circuit 1426A may include acapacitor C_(N). As such, each resonant circuit includes the capacitorC_(N) of the coupling circuit 1426A and the corresponding sense loop1622 a. The capacitor C_(N) is configured to reduce a variation of theresonant frequency by the multiplexer 1628 and further circuitry of thedetection circuit 1630. For example, the each capacitor C₁, C₂, C_(k),and C_(N) is configured to be a low pass filter configured attenuatefrequencies lower than the resonant frequency (e.g., attenuatefrequencies corresponding to the frequency of a field used for wirelesspower transfer). The capacitors further provide isolation betweencomponents of the detection circuit 1630 including the multiplexer 1628and the sense loops. The further components shown in FIG. 16 are similarto those described above with reference to FIG. 15. It is noted thatwith reference to the detection circuits 1530 and 1630 of FIGS. 15 and16 and other detection circuits as described below, the detectioncircuits 1530 and 1630 may be configured to measure a characteristicdependent on or a function of the resonant frequency of each of theresonant circuits including the sense loops. For example, in addition tomeasuring a frequency at which each resonant circuit resonates, aQ-factor or other characteristic may be measured and compared to storedcorresponding Q-factors or other corresponding characteristics of thenative resonant circuit (i.e., unchanged by external items) to determinethe presence of an object.

In some aspects, the embodiment shown in FIG. 16 may provide additionalbenefits. For example, the capacitance of each loop 1622 may removes thelow frequency component as induced by the strong magnetic field on thepad's surface prior to multiplexing, thus relaxing requirements on theanalog front-end circuitry, which preferably uses semiconductor (FET)type switches. It shall be appreciated that nonlinear distortion effectsmay occur in the analog multiplexer 1628 as the result of the lowfrequency induced that may reach several Volts. This is particularlytrue for multi-turn loops providing higher innate detection sensitivitybut also higher induced voltages. Each capacitor may reduce variation ofthe resonant frequency that may be caused by the multiplexer 1628.

In one aspect, temperature drift of the loops' resonant frequencies maybe unequal and specific for each sense loop therefore more difficult toassess and compensate for in the evaluation unit. Using capacitors withhigh temperature stability e.g., NP0 types, temperature drifts can beminimized and largely reduced to those of the sense loops.

With reference to FIG. 15 (and additionally applicable to FIG. 16), thehigh frequency oscillator 1546 for measuring the resonant frequency maybe a Numerically Controlled Oscillator (NCO). An additional signal 1550amplifier may be needed to generate sufficient sense current in theloops and as a buffer to provide a low impedance output (voltagesource-like output). The low impedance output may be advantages topreserve the Q-factor of the sense loop circuit and thus the slope ofthe phase function at resonance (see below).

At least one voltage and one current sensor 1544 and 1542 respectivelyis used to provide inputs for analyzing the impedance or phase functionof the sense loop 1522 a as seen at the input port of the resonantfrequency measuring unit 1534.

In an embodiment, the phase comparator 1548 may implement a heterodynereceiver approach e.g., by mixing the sense signals down to anarrow-band low intermediate frequency (IF) amplifier and performingphase comparison at IF. This approach may be chosen to increase thesignal-to-noise ratio and thus measurement accuracy.

The resonant frequency search may be performed by a swept frequencygenerator using the oscillator 1546 e.g., starting at a frequencysomewhat lower than the expected resonant frequency of the sense loop ofconcern and stopping the sweep when the differential phase reaches apredetermined value. To expedite the detection process and minimizeresponse time, particularly in case of a large sensor array, the startfrequencies may be derived from the reference values as used in theevaluation unit 1532, minimizing sweep range, thus minimizing sense timeper loop.

Instead of a swept frequency generator, an impulse generator (not shown)or any other pseudo-random noise generator may be used to analyze theimpedance function and measure the resonant frequency. Spectral analysistechniques such as Fourier Transform techniques (DFT, FFT, Gortzelalgorithm) and similar techniques operating in the numeric domain may beused. These techniques may require sampling and digitizing the sensesignals (voltage and current) using an adequate analog-to-digitalconverter.

To suppress sense loop induced transient noise as possibly generated bythe energy transfer system, sweeping or pulsing may be performed inintervals between the low frequency switching transients. This methodmay effectively reduce noise without extra filtering requirements.

The embodiments as described with reference to FIGS. 13-16 and furtherherein may be enhanced by adding temperature sensors (not shown) atdifferent places e.g., in the charging pad (below loop sensor array) andin the impedance measuring unit in order to increase stability againstambient temperature changes. Note that environmental requirements e.g.,−30 to +80° C. may apply for a metal object detection solution that isintegrated into an outdoor charging pad. Temperature as measured fromdifferent sensors may be used to pre-compensate measured impedance orresonant frequency values using a temperature model. Alternatively oradditionally, different stored reference values applicable in definedtemperature ranges may be used. These reference patterns may have beenproduced during manufacturing as part of a calibration procedure atdifferent pad and ambient temperature levels.

A method conceptually similar to the least mean square method describedabove may be used to compensate for ‘global’ changes in a measuredimpedance pattern e.g., due to temperature drift and circuit aging (seesection below).

Additionally, pattern recognition methods and artificial intelligencemay be employed to enhance detection performance and reduce false alarmprobability as is further described below.

Resonant Loops and Additionally Measuring their Q-factor

The embodiments described above with reference to FIGS. 14-16 describingdetection based on resonant frequency measurements may be furtherenhanced by additionally measuring the Q-factor of the sense loop 1522a. In case of a series-tuned loop, resonant frequency and Q-factorrepresent the complex ‘zero’ of the impedance function Z(f), which maybe expressed asp=−σ _(z) ±jω _(z)where σ_(p) and ω_(p) denote the dampening coefficient and the resonantfrequency, respectively.

The dampening coefficient relates to the Q-factor as follows:

$\sigma_{z} = \frac{\omega_{z}}{2Q}$

Measuring both to ω_(z) and σ_(z) may provide additional informationuseful to increase detection probability and reduce false alarmprobability.

There exist many ways to measure Q-factor using frequency domain and/ortime domain analysis techniques as already mentioned in section above.Measuring the slope of the phase or measuring the resistance atresonance may be examples.

Weakly Coupled Resonant Loops

As indicated above, in some aspects, the sense loop leads and the analogmultiplexers may excerpt a negative impact on the innate sensitivity ofthe loop impedance method. This may be particularly true for small loopse.g., 30×30 mm with 3-5 turns and a lead length e.g., above 0.5 m. Notethat loops may be made of very thin copper wire/traces to avoidsubstantial eddy current losses when exposed to the strong magneticfield used for wireless power transfer, which may be unfavorable inregards to the innate sensitivity.

Accuracy of the loop impedance method is related to the slope of thephase in the impedance function, which is in turn related to the loop'sQ-factor. A long lead to connect the loops to a central impedancemeasuring unit may decrease the Q factor and thus the slope of the phaseas it adds resistance. The lead may also add considerable inductance.Since the object normally changes only the loop inductance, the relativechange in overall impedance may become smaller with increasing leadlength. Moreover, temperature and aging stability of the sense circuitsmay worsen for long lead lengths.

Similar impairments degrading temperature stability and thus thesensor's accuracy and reliability can be attributed to the analogmultiplexers adding switch capacitance and significant resistance.

Therefore, the loop impedance method and the related loop resonancefrequency method as described above may require the analog multiplexerand the impedance measuring unit to be located as close as possible tothe loop array, meaning that active circuits may have to be integratedinto the charging pad 926. This may lead to challenging design problemsin considering the harsh environment, ground embedding, and MTBFrequired for infrastructure equipment. However, as indicated above, acapacitor, for example as shown with reference to FIG. 16, in someimplementations may be sufficient as a coupling circuit to reducevariation of the resonant frequency by the detection circuitry andmultiplexer.

Harmonics noise induced into sense loops at sense frequency may alsogenerally impair the sensor's accuracy.

In accordance with further embodiments, at least some of thesedeficiencies can be remedied by using the coupling circuit or network asdescribed above with reference to FIG. 14A. The coupling circuit 1426 isconfigured to reduce variation of resonant frequency of a resonantcircuit formed at least by a sense loop by the detection circuitincluding any lead lines. For an example, in accordance with anembodiment an array of weakly coupled resonant loops may be used. Weakcoupling may generally refer to coupling the sense loop to the detectioncircuit in a way that the detection circuit or any lead-lines from thedetection circuit to the sense loop reduce an impact on or reducealtering the resonant frequency and/or other electrical characteristicsof the sense loop. In some embodiments, loops may be either inductivelycoupled e.g., using a coupling loop or capacitively coupled e.g., usinga capacitive voltage divider. FIGS. 17A, 17B, and 17C are diagrams ofexemplary weakly coupled resonant sense loop configuration, inaccordance with exemplary embodiments. FIG. 17A shows a resonant senseloop 1722 a inductively coupled to a coupling loop 1726 a. The couplingloop 1726 forms at least portion of the coupling circuit 1426 asdescribed with reference to FIG. 14A. The coupling loop 1726 is thencoupled to a detection circuit as will be further described below. FIG.17B shows a resonant sense loop 1722 b that is capacitively coupledusing a capacitive voltage divider. FIG. 17C shows a sense loop 1722 cthat is self-resonant (e.g., the inherent capacitance of the sense loop1722 c to provide resonance at a distinct frequency) and is inductivelycoupled to a coupling loop 1726 c.

Inductive coupling may principally allow self-resonant loops asillustrated in FIG. 17C with no or only little extra capacitance, whichmay significantly simplify the loop array and reduce production costs.Here, winding capacitance is used to produce resonance requiring a highL-C ratio design or higher frequency e.g., >20 MHz. Self-resonant loopsmay be no more predominantly magnetic. They may produce significantE-field making the sensor sensitive to dielectric objects, which may beundesirable in some cases.

Weak coupling may effectively reduce the impact on the resonantfrequency and the Q-factor from the connecting leads and multiplexersthus increasing temperature and aging stability.

In some aspects, embodiments based on weakly coupling may providevarious benefits. The resonant frequencies and the Q-factor may mainlydepend on the sense loop's inductance L, loss resistance R and tuningcapacitor C. Thus a small change as produced by a foreign object maybecome fully effective and is no more compromised by parasitic elementsof the lead and the analog multiplexer circuitry. The slope of the phasefunction as seen by the impedance analyzer at resonance may be that ofthe resonant loop alone, therefore much steeper. Accuracy ofmeasurements in presence of noise may significantly improve as long asthe noise is comparatively small so that resonance can be reliablyidentified in the measured impedance function.

In a densely packed loop array, the resonant frequency of a sense loopmay be influenced by its direct neighbors. Such resonance detuning oreven resonance splitting effects may be particularly pronounced ifneighboring loops resonate at an equal or a similar frequency. Theseeffects however may not significantly impact sensitivity of this method.It may be useful to intentionally offset resonant frequencies ofadjacent loops as will be further described below. Resonant frequenciesmay be assigned following a frequency reuse pattern.

Loops may be tuned to a desired resonant frequency by design e.g., byappropriately choosing turn count, winding length and selecting acapacitor from a standard value series e.g., an E-series.

In a printed circuit board (PCB) implementation, the capacitor may beembedded into the epoxy of the PCB or mounted in small recesses so thatit is non-protrusive and well protected.

The effect of weak coupling may be explained using the equivalentcircuits as shown below for the case of inductive coupling. FIGS. 18Aand 18B are schematic diagrams of equivalent circuits 1800 a and 1800 bof an exemplary inductively coupled resonant sense loop 1822 a, inaccordance with an exemplary embodiment. The circuit 1800 a is comprisedof coupling loop 1826 a with lead inductance L_(c), coupling loop/leadloss resistance R_(c) (e.g., that may form a portion of a couplingcircuit 1426A). The capacitor C_(c) serves to suppress the low frequencymagnetic field induced voltage. At sense frequency however, the couplingloop 1826 a may be considered non-resonant. The actual sense loop 1822 ais composed of loop inductance L, loss resistance R and tuning capacitorC.

The circuit 1800 b of FIG. 18B is obtained by reducing the circuit 1800a at the top into the coupling loop 1826. Here the circuit 1800 b isshown as a transformed parallel-tuned L-C topology (L′, C′, R′)producing a pronounced and rapid change of impedance Z when sweepingfrequency over resonance. From the equivalent circuit 1800 b, theresonance and slope of phase at resonance are mainly determined by theelements of the sense loop. They are largely insensitive to theparameters of the coupling loop and the lead length.

FIG. 19 is a functional block diagram of an exemplary circuit 1900configured to detect an object using a coupling circuit 1926 between adetection circuit 1930 and a sense circuit 1922, in accordance with anexemplary embodiment. The circuit 1900 may include a sense circuit 1922having a sense loop and a capacitor C2 (or inherent capacitance ifself-resonant) so as to resonate at a distinct frequency (i.e., thecapacitor C2 and sense loop substantially determine the resonantfrequency). The circuit 1900 further includes a detection circuit 1930configured to measure a characteristic that depends on a currentresonant frequency of the sense circuit 1922 and configured to detectthe presence of an object in response to detecting a difference betweenthe measured characteristic and a corresponding reference characteristicdependent on the resonant frequency. As an example, the detectioncircuit 1930 may have one or more of the components as described abovewith reference to the detection circuit 1530 of FIG. 15 and may use anyof the methods and/or techniques described herein for detecting objectsbased on resonant frequency measurements. Furthermore, the circuit 1900includes a coupling circuit 1926 configured to reduce variation of theresonant frequency of the sense circuit 1922 by the detection circuit1930. For example, in an embodiment, the coupling circuit 1926 mayprovide weak coupling between the sense circuit 1922 and the detectioncircuit 1930. In the embodiment of FIG. 19, the capacitor C2 (orself-capacitance) and the sense loop alone form a resonant sense circuit1922 that may not include the coupling circuit 1926.

FIG. 20 is a functional block diagram of a circuit 2000 as shown in FIG.19 where the detection circuit 2030 is inductively coupled with a sensecircuit 2022 via a coupling loop 2026, in accordance with an exemplaryembodiment. As such, the coupling circuit 1926 of FIG. 19 may include acoupling loop 2026 optionally having a capacitance C1 that isconductively connected to the detection circuit 2030 and inductivelycoupled to the sense circuit 2022 including a sense loop and capacitanceC2. Stated another way, the sense circuit 2022 is galvanically isolatedfrom the detection circuit 2030. Operation of the coupling loop 2026 mayreduce variation of the resonant frequency of the sense circuit 2022 bythe detection circuit 2030 including any lead line from the detectioncircuit 2030 to the coupling loop 2026.

FIG. 21 is a functional block diagram of a circuit 2100 as shown in FIG.19 where the detection circuit 2130 is capacitively coupled with a sensecircuit 2122, in accordance with an exemplary embodiment. The circuit2100 includes a capacitive voltage divider including capacitors C1 andC2 between the sense circuit 2122 to form the coupling circuit 2126. Thedifference in size of the capacitors C1 and C2 may be provided such thatthe resonant frequency of the sense circuit 2122 (including a senseloop) is primarily defined by the smaller capacitor. The capacitorvoltage divider reduces variation of the resonant frequency of the sensecircuit 2122 by the detection circuit 2130 or any lead lines from thedetection circuit 2130 to the sense circuit 2122.

Embodiments using weak coupling as described above may principally allowfor much longer lead length. This may enable embodiments with a fullypassive sensor circuit in the charging pad 936 and with the activecircuits (foreign object detection electronics such as detection circuitas described above) integrated into a remotely located unit e.g., thecharging power supply unit 236 (FIG. 2).

In accordance with an embodiment, the following method may be used andimplemented by a detection circuit 1930 for measuring the resonantfrequency of the k-th sense loop at the input of the impedance analyzerunit (measurement port). However, as noted above, other characteristicsdependent on the resonant frequency may additionally be measured.

-   -   1. Measure the complex impedance function Z_(k)(f) over a        sufficiently large frequency range    -   2. Estimate the coupling loop/lead impedance by analyzing the        complex impedance function    -   3. Subtract the estimated coupling loop/lead impedance function        Z^_(c,k)(f) from the measured impedance function Z_(k)(f)    -   4. Identify the resonance of the sense loop 1922 in the        resulting differential impedance function        ΔZ_(k)(f)=Z_(k)(f)−Z^_(c,k)(f)    -   5. Measure frequency of the corresponding zero crossing of the        phase function arg{ΔZ_(k)(f)} or the imaginary part of the        impedance function Im{ΔZ_(k)(f)} and/or measure frequency of the        local maximum of the real part of the differential impedance        function Re{ΔZ_(k)(f)} that is produced at loop's resonance.

As already described above, the Q-factor or the dampening coefficientdefined as the real part of the complex pole frequencyP=−σp±jω _(p)may be measured additionally to enhance metal object detection based onthe weakly coupled approach.

Wiring complexity and the high number of analog switches that have to beprovided is another major issue of inductive sensing using a largenumber of sense loops. Therefore, methods reducing wiring and circuitcomplexity are desirable. This may be particularly true if a solutionwith a purely passive sensor network in the pad and a remotely locateddetection circuit is targeted.

In fact, the weakly coupled approach may have the potential tosignificantly reduce wiring and circuit complexity by combiningneighboring loops to groups (clusters), each group associated to asingle/common coupling network.

This new configuration called multiple coupled resonant loops maygenerally compromise coupling but may still provide sufficient couplingto unambiguously and accurately determine resonant frequency of each ofseveral loops individually.

FIG. 22 is a functional block diagram of an exemplary circuit 2200configured to detect an object using a coupling circuit between adetection circuit 2230 and a plurality of sense loops, in accordancewith an embodiment. The circuit 2200 includes several coupling networks(e.g., coupling circuits as described above with reference to FIGS. 19and 20) each including a coupling loop 2226 a, 2226 b, 2226 c, and 2226d. Each of the coupling loops 2226 a, 2226 b, 2226 c, and 2226 d areinductively coupled to a plurality of sense circuits each having a senseloop and capacitance (e.g., either self-capacitance or an addedcapacitor). For example, coupling loop 2226 a may form a couplingnetwork including a plurality of sense circuits including sense circuits2222 a 1 and 2222 aN (referred to herein collectively as 2222hereinafter). The coupling loops 2226 a, 2226 b, 2226 c, and 2226 d arecoupled to a multiplexer 2228 such that each of the coupling networks isselectively coupled to a detection circuit 2230 configured to measurethe resonant frequency of each sense circuit 2222 coupled to aparticular coupling loop 2226 a. The coupling loops 2226 a, 2226 b, 2226c, and 2226 d are each configured to reduce variation of the resonantfrequency of the each sense circuit 2222 by the detection circuit 2230.The detection circuit 2230 includes an impedance analyzer unit 2234 formeasuring resonant frequencies and an evaluation unit 2232 for comparingmeasured values with reference values and to determine informationregarding objects sensed via the sense circuits 2222. The sense circuits2222 may form a densely packed multi-dimensional array of loops in aplane configured to detect an object placed on a surface of the plane inwhich the sense circuits 2222 are configured. As noted above, detectioncircuit 2230 may measure other characteristic that are a function of theresonant frequencies of each of the sense circuits 2222.

In accordance with the embodiment shown in FIG. 22, a plurality of senseloops are therefore combined to a group that is associated to asingle/common coupling network. Furthermore, the sense loops 2222 aretuned to different resonant frequencies forming an impedance one portnetwork with distinct poles and zeros, whose relevant pole and/or zerofrequencies are distinguishable and measurable under operatingconditions.

Poles and zeros as resulting from such a network may be a highly complexfunction of each inductive and capacitive element including all crosscoupling effects (mutual inductances) as they may occur betweenneighboring loops in a densely packed array. A metal object placed ontop of such loop array generally changes some of the poles and zeros,which can be detected using an appropriate method e.g., comparingmeasured poles and zeros with a reference template. It should beappreciated that while FIG. 22 shows the sense circuits 2222 inductivelycoupled to the detection circuit via coupling loops 2226 a-d, the sensecircuits 2222 may be capacitively coupled based on a concept shown inFIG. 21 in accordance with another embodiment.

As described above, in an embodiment, each of the sense circuits 2222may be inherently configured to have a different resonant frequency inthe absence of any objects.

FIG. 23 is a functional block diagram of an exemplary circuit 2300configured to detect an object using a plurality of sense circuits 2322a and 2322 b (each having a sense loop) configured to have differentresonant frequencies, in accordance with an exemplary embodiment. Thecircuit 2300 includes sense circuit 2322 a having a capacitance C1 andsense circuit 2322 b having a capacitance C2 that may be different thanC1. Each sense circuit 2322 a and 2322 b may therefore natively have aparticular frequency for which the sense loop 2322 a and 2322 b isresonant. The circuit 2300 includes a detection circuit 2330 configuredto measure a characteristic that is a function of the resonant frequencyof each of the sense circuits 2322 a and 2322 b to determine thepresence or absence of an object. The detection circuit 2330 mayimplement and or include one or more of the techniques and components asdescribed above, for example with reference to FIGS. 13-22. The circuit2300 includes coupling circuit 2326 coupled between the detectioncircuit 2330 and the sense circuits 2322 a and 2322 b. In someembodiments, the coupling circuit 2326 is configured to reduce variationof the resonant frequencies of the sense circuits 2322 a and 2322 b bythe detection circuit 2330 including any lead lines. By using multiplesense circuits 2322 a and 2322 b, the sensitivity of the detectionsystem may increase such that the detection circuit 2330 is configuredto measure a position of an object relative to a position of the sensecircuits 2322 a and 2322 b such that the system may detect the positionof an object within the system.

Using sense circuits 2322 a and 2322 b with different resonantfrequencies may allow for improving sensitivity and reducing complexity.For example, FIG. 24 is a functional block diagram of a circuit 2400 asshown in FIG. 23 where the detection circuit 2430 is inductively coupledto sense circuits 2422 a and 2422 b having different resonantfrequencies, in accordance with an exemplary embodiment. The detectioncircuit 2430 may be configured to measure the current resonantfrequencies of both of the sense circuits 2422 a and 2422 b when drivingthe coupling loop 2426. This may allow for reduced complexity andimproved sensitivity as, for example resonant frequencies of a largenumber of sense circuits 2422 a and 2422 b may be measured via driving asingle coupling loop 2426.

Regardless of the coupling type, the coupling network may be configuredto provide optimum and similar coupling to each loop of a group.

In an embodiment, each loop 2222 of a group may be part of the outercontour/perimeter of that group having at least one side/edge on thecontour/perimeter line. The group may be encompassed by a coupling loopessentially going along the contour/perimeter of that group. Singlecolumn or a double column of loops as shown in the figure below arepossible configurations. Coupling may be intentionally reduced for thoseloops that have more than one edge/side on the contour/perimeter line.This may be accomplished by cropping corners of the coupling loop.

FIGS. 25A, 25B, 25C, 25D, 25E, and 25F are diagrams of exemplaryconfigurations sense loop arrays inductively or capacitivley coupled toa detection circuit, in accordance with an exemplary embodiment. For anexample, an embodiment of a sense loop array may be derived from thesingle loop coupling as shown in FIG. 25A. FIG. 25A includes a couplingloop 2526 a inductively coupled to a multi-dimensional array of senseloops including sense loop 2522 a 1 and 2522 a 2. FIG. 25B shows anotherconfiguration where a coupling loop 2526 b is inductively coupled to acolumn of single sense loops including sense loop 2522 b 1 and senseloop 2522 b 2. FIG. 25C shows another embodiment of a coupling loop 2526inductively coupled to a row of sense loops including sense loop 2522 c1 and sense loop 2522 c 2. The configuration depicted in FIG. 25C alsomay provide substantially equal coupling factor to each sense loop 2522c 1 and 2522 c 2. Linear rows, meander-shaped or serpentine-shapedarrangements of loops may be connected to a group.

Other arrangements e.g., triple column of loops with the coupling loopnot in proximity of all of the sense loops show weaker coupling to theloops in the center. In one aspect, this technique may be used if theloop array is integrated into the enclosure of a magnetic padadditionally attenuating the magnetic field in the center of thecoupling loop.

The concept of multiple inductively coupled resonant loops may beexpanded to hierarchical (concatenated) structures comprised of groupsand subgroups. A group may be formed by a plurality of resonant loopsoperationally coupled to a coupling loop. The resonant loops of thisgroup in turn may serve as coupling loops for resonant loops belongingto subgroups (lower hierarchy level), and so on.

Alternatively, multiple loops 2522 d 1 and 2422 d 2 may be coupledcapacitively to a single feed line 2526 d using the capacitive voltagedivider as shown in FIG. 25D. The resulting topology that is shown inFIG. 25D may be considered as the electrically dual topology of themultiple inductively coupled resonant loops. Each sense loop 2522 d 1and 2522 d 2 in FIG. 25D is coupled in series with a capacitor 2525 d 1and 2525 d 2, respectively, to form a resonant circuit (i.e., they areseries tuned). The sense loop 2522 d 1 and capacitor 2525 d 1substantially determine the resonant frequency. A coupling capacitor2527 d common to all sense loops 2522 d 1 and 2522 d 2 is coupled inparallel with the resonance capacitors 2525 d 1 and 2525 d 2 to form acapacitive voltage divider. In one aspect, the coupling capacitor 2527 dis the “larger” capacitor while each of the resonance capacitors 2525 d1 and 2525 d 2 are the “smaller” capacitors. It is noted that withreference to FIG. 14A, a coupling circuit 1426A may include the couplingcapacitor 2527 d while each sense circuit may include the series tunedsense loop 2522 d 1 with resonance capacitor 2525 d 1.

FIG. 25E is another topology using a capacitive voltage divider toprovide a weak coupling in accordance with an embodiment. In this case,each sense loop 2522 e 1 and 2522 e 1 are parallel tuned using resonancecapacitors 2525 e 1 and 2525 e 2, respectively. The sense loop 2522 e 1and resonance capacitor 2525 e 1 substantially determine the resonancefrequency. A coupling capacitor 2527 e common to all sense loops 2522 e1 and 2522 e 2 is coupled in series with resonance capacitors 2525 e 1and 2525 e 2. In one aspect, the coupling capacitor 2527 e is the“larger” capacitor while each of the resonance capacitors 2525 d 1 and2525 d 2 are the “smaller” capacitors. It is noted that with referenceto FIG. 14A, a coupling circuit 1426A may include the coupling capacitor2527 e while each sense circuit may include the parallel tuned senseloop 2522 e 1 with resonance capacitor 2525 e 1.

FIG. 25F is another topology using a capacitive voltage divider toprovide a weak coupling in accordance with an embodiment. In this case,each sense loop 2522 f 1 and 2522 f 1 are parallel tuned using resonancecapacitors 2525 f 1 and 2525 f 2, respectively. The sense loop 2522 f 1and resonance capacitor 2525 f 1 substantially determine the resonancefrequency. Coupling capacitors 2527 f 1 and 2527 f 2 are included foreach sense loop 2522 f 1 and 252 ssf 2 such that each is connected inparallel with resonance capacitors 2525 f 1 and 2525 f 2, respectively.In one aspect, each coupling capacitor 2527 f 1 and 2527 f 2 are the“larger” capacitors while each of the resonance capacitors 2525 d 1 and2525 d 2 are the “smaller” capacitors. It is noted that with referenceto FIG. 14A, there may be multiple coupling circuits that each includecoupling capacitors 2527 f 1 and 2527 f 2 while each sense circuit mayinclude the parallel tuned sense loop 2522 e 1 with resonance capacitor2525 e 1.

Other e.g., mixed coupling topologies are also possible.

FIGS. 26A, 26B, 26C, 26D, 26E, and 26F are schematic diagrams ofexemplary equivalent circuits 2600 a and 2600 b of an inductively andcapacitively coupled resonant loop array, in accordance with anexemplary embodiment. The circuit 2600 a includes a coupling loop 2626 aincluding a low frequency suppressing capacitor C_(c), the couplingloop's/lead's inductance L_(c) and loss resistance R_(c). The circuit2600 a includes multiple sense loops 2622 a 1 and 2622 a 2 including theL, C, R elements as well as the mutual inductance (coupling coefficient)between coupling loop and each resonant loop. Other possible crosscouplings are neglected.

As already described above, the resonant circuits 2622 a 1 and 2622 a 2may be reduced to the primary side (coupling loop) resulting in anequivalent circuit 2600 b that may be approximately represented as shownin FIGS. 26B. Here again, each resonant loop 2622 a 1 and 2622 a 2appears as a parallel resonant circuit whose response are visible in theimpedance function Z(f).

FIG. 26C is an equivalent schematic diagram of the sense loopconfiguration shown in FIG. 25D. As shown each sense circuit comprisinginductance 2522 c 1 and capacitance 2525 c 1 is series tuned and allsense circuit are coupled to a common coupling capacitor 2527 c inparallel. FIG. 26D is an equivalent schematic diagram of the sense lopconfiguration shown in FIG. 25E where each sense circuit comprisinginductance 2522 d 1 and capacitance 2525 d 1 are parallel tuned and eachsense circuit is coupled the common coupling capacitor 2527 d in series.FIG. 26E is an equivalent schematic diagram of the sense loopconfiguration shown in FIG. 25F where each sense circuit comprisinginductance 2522 e 1 and capacitance 2525 e 1 are parallel tuned andcoupled to each coupling capacitor 2527 e 1 and 2527 e 2 in parallel.Furthermore, FIG. 26F is an equivalent schematic diagram of anothersense loop configuration where each sense circuit comprising inductance2522 f 1 and 2522 f 2 and capacitance 2525 f 1 and 2525 f 2 are seriestuned and coupled to each coupling capacitor 2527 f 1 and 2527 f 2 inseries. It is noted that in any of the above topologies, either aself-resonant loop may be used having the resonance capacitance inherenttherein or an added resonance capacitor may be added.

In accordance with an embodiment, a detection circuit may implement thefollowing method for measuring the resonant frequencies of the k-tharray/group of inductively coupled resonant sense loops at the input ofthe impedance analyzer unit 2234 (FIG. 22) (measurement port). However,as noted above, other characteristics dependent on the resonantfrequency may additionally be measured.

-   -   1. Measure the complex impedance function Z_(k)(f) over a        sufficiently large frequency range    -   2. Estimate the coupling loop/lead impedance by analyzing the        complex impedance function    -   3. Subtract an impedance function Z^_(c,k)(f) from the measured        impedance function Z_(k)(f). The impedance function Z^_(c,k)(f)        may include the estimated coupling loop/lead impedance function        and other correction function as needed to optimally perform the        following steps.    -   4. Identify resonances of each sense loop in the resulting        differential impedance function ΔZ_(k)(f)=Z_(k)(f)−Z^_(c,k)(f)    -   5. Measure all frequencies of the corresponding zero crossings        of the phase function arg{ΔZ_(k)(f)} or the imaginary part of        the impedance function Im{ΔZ_(k,n) (f)} and/or measure all        frequencies of the local maxima of the real part of the        differential impedance function Re{ΔZ_(k)(f)} that are produced        at loops' resonances.

FIG. 27 is a plot 2700 showing a phase response of an inductivelycoupled resonant loop array before and after compensating for animpedance of a coupling loop, in accordance with an exemplaryembodiment. FIG. 27 illustrates the procedure of subtracting theestimated coupling loop/lead impedance and measuring the resonantfrequencies in the phase function of the resulting differentialimpedance function.

A similar method/procedure may apply for a capacitively coupled looparray. Instead of searching local maxima in Z_(k)(f), item 5 is modifiedto local minima of the real part of the differential impedance functionRe{ΔZ_(k)(f)} and determine the minima as produced by each sense loop'sresonance.

Computing and evaluating of at least one of a first, second, and thirdderivative of the impedance function may also be useful to identifypositions of poles/zeros of the impedance function Z_(k)(f).

As already described in a subsection above, the Q-factors or thedampening coefficients defined as the real part of the complex poles orzeros of the impedance function Zk(f)p _(k,i)=−σ_(p,k,i) ±jω _(p,k,i), or z _(k,i)=−σ_(z,k,i) ±jω _(z,k,i)respectively, may be measured additionally for each resonance ω_(k,i) toenhance metal object detection based on the multiple coupled resonantloop approach.

As already mentioned above, switching noise may be induced into thesense loops. To maximize signal-to-noise ratio and thus measurementaccuracy at resonance frequencies, a current source-like high frequencygenerator may be used to measure Z_(k)(f) in case of inductive coupling,whilst for capacitive coupling, a voltage source-like generator ispreferably employed. This approach avoids measuring impedance in currentminima thus at low signal-to-noise ratio. The coupling loop/lead'sinductance may already suffice to mimic a current source-likecharacteristic provided that the HF source generates enough highvoltage.

As described above, for example with reference to FIGS. 23 and 24,assigning resonant frequencies to sense loops may also be provided.Preferably, resonant frequencies (poles/zeros) of sense loops belongingto the same group are adequately and smartly spaced apart so that theycan be easily identified and accurately measured. This assignment maytake into account the Q-factor of the sense loops, design constraints ofthe impedance analyzer circuits, bandwidth constraints, noise andenvironmental disturbance effects, as well as detuning effects that mayoccur when integrated the sense loop array into the target magnetic pad.

For example, for a sense loop size of 35×35 mm, a Q-factor in the rangefrom 50-80 may be achieved corresponding to a 3 dB fractional bandwidthof 0.02-0.013. Assuming a total fractional bandwidth of 1 for a highfrequency sensing system operating e.g., in the range from 5 to 15 MHz,up to about 40 resonant frequencies may be allocated e.g., equidistantlyspaced. These resonant frequencies may have to be selectively assignedto loops and groups of loops in order to optimally use and reuse theavailable bandwidth in different groups of loops. The number of loopsper group may be the result of a trade-off between complexity anddetection sensitivity.

According to an embodiment, the number of loops per group may varybetween 20 and 30 given the above example of an available bandwidth.Thus, a complexity reduction in wiring and multiplexing up to a factorof 30 may be expected.

Measuring bandwidth may be expanded towards even higher frequencies. Itshall be noted however, that sensitivity on dielectric objects (e.g.,water, snow, ice, foliage) may also increase. This undesirable effectmay be diminished by a lower turn count for those sense loops/coilstuned to upper edge frequencies. This may result in single turn loops inthe end. Multi-turn loops are considered most appropriate at lowerfrequencies e.g., <10 MHz if maximum Q-factor has to be targeted.

FIG. 28 is a functional block diagram of an exemplary apparatus 2800 fordetecting an object integrated within a inductive charging pad 2802configured to wirelessly transmitting power, in accordance with anexemplary embodiment. The inductive charging pad 2802 includes anelectrically conductive structure 2804 (e.g., an induction coil 104 a asdescribed above with reference to FIG. 1) that is configured towirelessly transmit power via a magnetic field at a level sufficient topower or charge a load. The apparatus 2800 includes an array of senseloops 2822 a, 2822 b (hereinafter 2822) for detecting objects may beprovided across the surface of the pad 2802. The array of sense loops2822 may include coupling loops such as loop 2826 configured toinductively couple multiple sense loops 2822 a and 2822 b to a detectioncircuit 2830 via a lead line shown in cable 2850. The detection circuit2830 may be integrated within a charging power supply unit 2836. Asshown in FIG. 28, the multiple coupled resonant loop approach mayprovide solutions that integrate an entirely passive sensor network intothe charging pad 2802 requiring considerable reduction of wiringcomplexity. A bundle of twisted pair lines e.g., a PSTN cable may beused to connect the resonant sense loop array to the multiplexer thatmay be part of the remotely located detection circuit 2830 (i.e.,foreign object detection electronics). A non-entirely passive solutionwith a multiplexer on the charging pad may also be provided according toanother embodiment. It is noted that the apparatus 2800 may be adaptedto use any of the sense loop/coupling circuit configurations of FIGS.14-24.

Coupled Resonator Filter

Forming a propagation medium (transmission line) using canonicalstructures of coupled resonant loops may be another approach to metalobject detection. FIG. 29 is a functional block diagram of an exemplaryinductively coupled resonant filter 2900 for detecting objects, inaccordance with an exemplary embodiment. FIG. 29 shows an embodimentusing inductively coupled wire loops 2922 a and 2922 b. The circuit 2900may be also considered as a high order filter with an inductivelycoupled input and output terminal 2926. Resonators may be all tuned tothe same frequency or to slightly different frequencies as required foroptimum sensitivity and detectability of an object.

Here, metal objects may be detected by measuring reflectioncharacteristics at port 1 and/or port 2 and/or transmissioncharacteristics between port 1 and port 2, which may change in presenceof a metal object.

Other structures combining the multiple coupled resonant loop approachwith the coupled resonator filter approach, or topologies usingcapacitive coupling may also be provided. Loop structures extending intwo or three dimensions and defining multiple measuring ports are alsopossible.

Evaluation (Post-processing) Methods and Procedures

As illustrated in conceptual diagrams above, the output of a magneticfield or impedance analyzer may have to be further processed in anevaluation unit (e.g., evaluation unit 2232 of FIG. 22) of a detectioncircuit. With reference to FIG. 22, for example, besides subtractingreference/calibration values and making decisions, the evaluation unit2232 may perform a modification on the measurement samples as deliveredby the analyzer unit. This modification may be part of a post processingmethod. An example of such a modification and a method is provided abovefor the case of the magnetic field sensing method (least mean squaremethod).

Similar methods may be also employed to enhance the loop impedance orloop resonant frequency sensing approach to compensate for residualeffects e.g., from the vehicle pad, vehicle's underbody structure,temperature drift, dielectric objects (water, snow, ice, foliage),aging, etc.

These residual effects may be recognized in the patterns that areproduced if measured values/samples are mapped onto a 2-dimensionalarray according to the array of loop sensors resulting in a2-dimensional value matrix consisting of rows and columns.

By using artificial intelligence including neuronal networks, fuzzylogic, etc., such effects may be effectively compensated or cancelledout increasing detection probability and/or reducing false alarmprobability of the metal object detector.

Such methods may include detecting metal objects in their context orbackground pattern rather than using absolute detection criteria, e.g.,automatically assessing the detection threshold and detection rulesbased on the back ground pattern.

If the pattern appears noisy, meaning that time sequentially acquiredpatterns show a variance, a temporal and/or a spatial averagingtechnique may apply e.g., moving average, exponential decay averaging(e.g., 1^(st) order infinite response filter) over sequentially acquiredpatterns and/or spatial filtering/smoothing.

The decision threshold may be set lower e.g., for detectingsudden/abrupt and local changes in a measured pattern since such changesare unlikely to occur from temperature drift and aging or from a vehicleparking on the charging pad. This approach may provide increasedsensitivity for detecting objects that enter the critical space when FODis active.

Spatial interpolation over the array of samples e.g., over rows andcolumns may enhance detection particularly for small objects that areplaced on corners or edges of sense loops where innate sensitivity maybe lower. Using interpolation, an object positioned in the corner offour adjacent loops may provide a similar response as a coin positionedin the center of a loop.

Moreover, information from other sensors, vehicle positioning system,vehicle detection and identification system, power and efficiencymeasurements (power budget) on the energy transfer system may be takeninto account in the pattern recognition and decision process.

Joint use of different detection techniques, methods, procedures asdescribed above may provide solutions with enhanced detectionsensitivity, reliability and/or resilience to environmental impacts. Forexample, the loop induced voltage may be combined with the loopimpedance measuring method, or any of the inductive sensing method maybe combined with at least one of an optical, acoustical, or uW sensingmethod.

Trouble Shooting and Recalibration Methods and Procedures

Embodiments further may provide for trouble shooting and recalibrationof an object detection system.

It may happen over the years that one or more loops of a pad integratedloop array may break or modify its impedance e.g., due to mechanical orenvironmental impacts (damage), mechanical stress, aging or by otherreasons. Impedance as measured at these loop ports in such event may becompletely out of range or may mimic a foreign object that is actuallynot present.

Such a fault event may be detected and reported to a central managementsystem of an infrastructure operator or to an electronic device of theuser/owner of the system if installed e.g., in a home garage. Reportingmay be via standard communications links as they may be available tomonitor and manage a charging infrastructure.

The following trouble shooting and recalibration method may apply:

-   -   1. Request visual inspection of the charging pad by a service        personnel/trouble shooter (in case of public infrastructure) or        by the user/owner of a privately owned system    -   2. Check if the pad is clean from any metal object    -   3. Interrogate system to get error status info about failed loop        sensors and how many loops are out of spec    -   4. If number of failed loops does not exceed permitted number        and if failed loops do not form unacceptable clusters,        recalibrate the FOD system, else initiate replacement of the pad

Other pads of a charging infrastructure that do not signal faults maynot need periodic recalibration and maintenance.

In contrast to implementations using inductive sensing, other types ofsystems may be provided in accordance with other embodiments. Microwaveor Millimeter wave radar sensing for object detection is used insecurity systems described in Li, Yong, et. al, “A microwave measurementsystem for metallic object detection using swept-frequency radar”,Millimetre Wave and Terahertz Sensors and Technology, Proc. of SPIE Vol.7117 71170K-1, 2008. Ultra high frequencies e.g., in the Terrahertzrange and ultra wide processing bandwidth may be used to resolve a smalland thin object e.g., a coin placed on a surface. Microwave radartechniques in general may however be useful to detect small hazardousobjects, which are not located on a solid surface but elsewhere in thespace between the primary and secondary magnetic structure (air gap).Similarly to active acoustic sensing, electromagnetic waves arereflected or scattered by a foreign object and may be detected by amicrowave sensor array that is integrated in the peripheral area of anenergy transfer pad. Propagation delay may be used as a criterion todistinguish a foreign object from reflections of the ground, theadjacent magnetic pad, or the vehicle's underbody structure. However,this method may not be able to distinguish metal objects from othersolid but non-hazardous objects.

In another embodiment, microwave sensing may use the vibration of metalobjects as a peculiar characteristic to distinguish metal objects fromnon-metal objects. A metal object exposed to a strong alternatingmagnetic field vibrates at a frequency twice that of the magnetic field.If irradiated by a microwave source, this vibration causes a micro-phase(frequency) modulation in the reflected or scattered waves. Thismicro-Doppler effect may be visible as two weak responses at frequenciesf _(1,2) =f _(c) ±f _(m)

where f_(m) denotes the magnetic field frequency and f_(c) the microwavecarrier frequency. In other words, metal objects may be detected bytheir characteristic signature in the Doppler frequency domain.

This microwave-Doppler-based approach may be supplemented by a magneticpulse generator. A strong enough magnetic pulse will shake a metalobject causing a more pronounced Doppler response. Such a magnetic pulsemay be generated by temporarily connecting a high voltage pulsegenerator to the magnetic structure as used for the inductive energytransfer. A high current pulse may be generated by charging a large highvoltage capacitor and discharging it directly via the pad's coil. Thismethod may consume considerable amount of energy and may produce an EMCissue if continuously applied e.g. by periodic pulsing. However, it mayserve temporarily for a relatively short period of time as a second(post detection analysis) method for substantiating a positive detectionhypothesis that was obtained using a first method. The first method thatis continuously running may use at least one of a method describedabove. This two stage approach to foreign object detection may provideimproved reliability (higher detection probability and/or lower falsealarm probability).

FIG. 30A is a functional block diagram of another exemplary system 3000for detecting an object 3024, in accordance with an exemplaryembodiment. The system includes a power source 3008, a base chargingsystem power converter 3036 and a transmit circuit 2006 including a basesystem induction coil 3004 as described above with reference to FIG. 2.These components may form, at least in part, a power circuit configuredto generate a magnetic field and transfer power wirelessly at a levelsufficient to power or charge, for example, an electric vehicle via themagnetic field. The system further includes a detection circuit 3030configured to transmit signals and detect a frequency of vibration of anobject 3024 based on a reflection of signal. For example, the detectioncircuit 3030 may be configured to transmit microwave signals andconfigured to detect a frequency of vibration based on a micro-Dopplereffect as described above. For example, the detection circuit 3030 maybe configured to detect an object 3024 is metal based on a particularfrequency of vibration (e.g., twice the frequency of the alternatingcurrent of the power source 3008 used to generate the alternatingmagnetic field at the frequency). The system 3000 further includes amagnetic pulse generator 3062 configured to generate a magnetic pulsestronger than the magnetic field generated by the power circuit. Thismay be done in response to initially detecting an object. After thepulse is generated, the detection circuit may be configured to 3030re-detect the frequency of vibration of an object 3024 to confirm apositive detection of a metal object 3024 based on the detectedfrequency.

According to this embodiment, the magnetic field generated may beleveraged to further provide a magnetic field for detection of objects.Using the existing magnetic field used for power transfer, the detectioncircuit 3030 may be configured to detect vibration of objects toidentify metal objects.

FIG. 30B is a functional block diagram of a detection circuit 3030 ofthe system of FIG. 30A, in accordance with an exemplary embodiment. Asshown, the detection circuit 330 includes several sensors 3064 a and3064 b that may form an array covering some area, for examplecorresponding to an area above a charging pad. Each of the sensors 3064a and 3064 b may be configured to transmit signals and each determines afrequency of vibration of an object along with other information basedon reflected signals. In this way spatial resolution may be providedallowing the detection circuit 3030 to be able to determine a type,shape, or distance of the object from the detection circuit. As such anarray of sensors is provided to provide for spatial resolution to allowfor detecting various characteristics of an object to be detected. Inone sense, an “image” of the pad may be provided using an array ofsensors. As the pad itself may vibrate from the magnetic field, thearray of sensors may allow for distinguishing the pad and other objects.Stated another way, a three-dimensional “microwave” image may beprovided to detect objects throughout the space between a pad and anarea for detecting.

In addition, as mentioned above, the embodiments described above may beused in a variety of different applications. For example, an embodimentaccording to those described above may be configured to detect anabsence of an object, for e.g., an anti-theft system. For example, thedetection circuit and sense loops may be placed proximate an object andconfigured to detect if the object has been removed based on a change inan electrical characteristic of the sense loop. More particularly, asanother example, the detection circuit may be configured to detect thata frequency at which a sense loop resonate changes when the object isremoved. In this case the reference resonant frequency may be thefrequency at which the sense loop resonates in the presence of anobject.

FIG. 31 is a flowchart of an exemplary method 3100 for detecting thepresence of an object, in accordance with an exemplary embodiment. Atblock 3102, a signal is applied to a resonant circuit having a resonantfrequency. The resonant circuit includes a sense circuit including anelectrically conductive structure. A coupling circuit is coupled to thesense circuit. At block 3104, the presence of an object is detected viaa detection circuit coupled to the sense circuit via the couplingcircuit in response to detecting a difference between a measuredcharacteristic that depends on a frequency at which the resonant circuitis resonating and a corresponding characteristic that depends on theresonant frequency of the resonant circuit. The coupling circuit isconfigured to reduce a variation of the resonant frequency by thedetection circuit in the absence of the object. In an embodiment, themethod 3100 may be performed by the circuit 1400A.

FIG. 32 is a functional block diagram of an apparatus 3200 for detectingthe presence of an object, in accordance with an exemplary embodiment.The apparatus 3200 includes means 3202, 3204, and 3206 for the variousactions discussed with respect to FIGS. 1-29.

FIG. 33 is a flowchart of an exemplary method 3300 for detecting thepresence of an object in a magnetic field, in accordance with anexemplary embodiment. At block 3302, a magnetic field is generated andpower is transferred wirelessly at a level sufficient to power or chargea load via the magnetic field. The magnetic field causes a vibration ofan object. At block 3304, signals are transmitted and a frequency ofvibration of the object caused by the magnetic field is detected basedon a reflection of the transmitted signals.

FIG. 34 is a functional block diagram of an apparatus for detecting thepresence of an object in a magnetic field, in accordance with anexemplary embodiment. The apparatus 3400 includes means 3402 and 3404for the various actions discussed with respect to FIGS. 30A, 30B, and33.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations. Forexample, a means for generating a magnetic field may comprise an antennaor other conductive structure. A means for resonating may comprise aresonant circuit. A means for detecting may comprise a detection circuitor other controller. A means for reducing variation of a resonantfrequency may comprise a coupling circuit.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative logical blocks, modules, circuits, and methodsteps described in connection with the embodiments disclosed herein maybe implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. The described functionalitymay be implemented in varying ways for each particular application, butsuch implementation decisions should not be interpreted as causing adeparture from the scope of the embodiments.

The various illustrative blocks, modules, and circuits described inconnection with the embodiments disclosed herein may be implemented orperformed with a general purpose processor, a Digital Signal Processor(DSP), an Application Specific Integrated Circuit (ASIC), a FieldProgrammable Gate Array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method and functions described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on a tangible,non-transitory computer-readable medium. A software module may reside inRandom Access Memory (RAM), flash memory, Read Only Memory (ROM),Electrically Programmable ROM (EPROM), Electrically ErasableProgrammable ROM (EEPROM), registers, hard disk, a removable disk, a CDROM, or any other form of storage medium known in the art. A storagemedium is coupled to the processor such that the processor can readinformation from, and write information to, the storage medium. In thealternative, the storage medium may be integral to the processor. Diskand disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer readable media. The processor andthe storage medium may reside in an ASIC. The ASIC may reside in a userterminal. In the alternative, the processor and the storage medium mayreside as discrete components in a user terminal.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features s have been described herein. It is to be understoodthat not necessarily all such advantages may be achieved in accordancewith any particular embodiment. Thus, the invention may be embodied orcarried out in a manner that achieves or optimizes one advantage orgroup of advantages as taught herein without necessarily achieving otheradvantages as may be taught or suggested herein.

Various modifications of the above described embodiments will be readilyapparent, and the generic principles defined herein may be applied toother embodiments without departing from the spirit or scope of theinvention. Thus, the present invention is not intended to be limited tothe embodiments shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. An apparatus for detecting a presence of anobject, the apparatus comprising: a plurality of resonant sensecircuits, each having a resonant frequency, each resonant sense circuitcomprising an electrically conductive structure and a coupling circuitconfigured to determine resonance and an amount of coupling, theelectrically conductive structure comprising a loop positioned within amultidimensional loop array; a multiplexer coupled to the plurality ofresonant sense circuits; at least one capacitor coupled between theplurality of resonant sense circuits and the multiplexer; and adetection circuit coupled to the multiplexer, the detection circuitconfigured to detect the presence of the object in response to detectinga difference between a measured characteristic that depends on afrequency at which a resonant sense circuit of the plurality of resonantsense circuits is resonating and a corresponding characteristic thatdepends on the resonant frequency of the resonant sense circuit.
 2. Theapparatus of claim 1, wherein each coupling circuit comprises one of: acapacitor electrically connected between the electrically conductivestructure and the multiplexer, the resonant sense circuit comprising thecapacitor and the electrically conductive structure; at least onecapacitor and a coupling loop electrically connected to the multiplexer,the coupling loop inductively coupled to the electrically conductivestructure; or a capacitive voltage divider configured to capacitivelycouple the multiplexer to the resonant sense circuits.
 3. The apparatusof claim 2, wherein the coupling circuit is configured to reduce avariation of the resonant frequency by the multiplexer in the absence ofthe object, the capacitor further configured to attenuate electricalsignals having frequencies lower than the resonant frequency.
 4. Theapparatus of claim 2, wherein each resonant sense circuit comprises anelectrically conductive structure, a capacitor electrically connected tothe electrically conductive structure, the electrically conductivestructure comprising an inductor, and wherein the capacitor and theelectrically conductive structure substantially form the resonantcircuit and substantially determine the resonant frequency.
 5. Theapparatus of claim 2, wherein the capacitive voltage divider comprises afirst capacitor and a second capacitor, wherein each resonant sensecircuit comprises the first capacitor that is coupled to theelectrically conductive structure that comprises an inductor, whereinthe first capacitor and the electrically conductive structuresubstantially form the resonant circuit and substantially determine theresonant frequency, the second capacitor determining an amount ofcoupling between the resonant sense circuit and the detection circuit.6. The apparatus of claim 2, wherein each resonant sense circuitcomprises an electrically conductive structure, a capacitor electricallyconnected to the electrically conductive structure, the electricallyconductive structure comprising an inductor, and wherein the capacitorand the electrically conductive structure substantially form theresonant sense circuit and substantially determine the resonantfrequency, and wherein the electrically conductive structure isinductively coupled to the multiplexer, determining an amount ofcoupling between the resonant sense circuit and the detection circuit.7. The apparatus of claim 1, wherein the measured characteristiccomprises at least one of a measured resonant frequency or a measuredquality factor (Q-factor) of the resonant circuit, and wherein thecorresponding characteristic is at least one of the resonant frequencyor the Q-factor of the resonant circuit.
 8. The apparatus of claim 1,wherein the multiplexer comprises a lead line electrically connected tothe coupling circuit, and wherein the coupling circuit is furtherconfigured to reduce a variation of the resonant frequency by the leadline in the absence of the object.
 9. The apparatus of claim 1, whereinthe plurality of electrically conductive structures comprise a firstelectrically conductive structure and a second electrically conductivestructure, different from the first electrically conductive structure,the second electrically conductive structure configured to wirelesslytransmit power via a magnetic field at a level sufficient to power orcharge a load.
 10. The apparatus of claim 9, further comprising atransmit circuit configured to apply an alternating current to thesecond electrically conductive structure at a frequency, wherein theresonant frequency of the resonant circuit is higher than the frequencyof the alternating current.
 11. The apparatus of claim 9, wherein thefirst electrically conductive structure comprises a first loop defininga first plane, wherein the second electrically conductive structurecomprises a second loop defining a second plane substantially parallelwith the first plane, wherein the first loop is positioned over at leastone of an area enclosed by the second loop or overlapping the secondloop.
 12. The apparatus of claim 11, wherein the loops of the pluralityof sense circuits positioned in the multi-dimensional loop arraycollectively defining a third plane, and wherein the loops collectivelycover at least the area enclosed by the second loop.
 13. The apparatusof claim 12, wherein a diameter of each of the loops of the plurality ofresonant sense circuits is substantially equal to or less than tenpercent of a diameter of the second loop.
 14. The apparatus of claim 12,wherein a diameter of each of the loops of the plurality of sensecircuits is substantially equal to or greater than twice a size of theobject.
 15. The apparatus of claim 12, wherein the detection circuit isfurther configured to detect the presence of the object in response todetecting a difference between respective measured characteristics thatdepend on frequencies at which each of the resonant sense circuits areresonating and corresponding characteristic that depend on therespective resonant frequencies.
 16. The apparatus of claim 1, whereinthe measured characteristic comprises a measured resonant frequency, andwherein the detection circuit is configured to measure an impedanceresponse of the resonant sense circuit over a range of frequenciesincluding the resonant frequency and configured to determine themeasured resonant frequency based on the impedance response.
 17. Theapparatus of claim 1, wherein the measured characteristic comprises ameasured resonant frequency, wherein the detection circuit comprises atleast one of: a swept frequency generator configured to drive theresonant circuit with a signal over a range of frequencies and stoppingdriving the resonant circuit when resonance is detected to determine themeasured resonant frequency; a pulse generator configured to measure afrequency response of the resonant circuit to determine the measuredresonant frequency; or a pseudo-random noise generator configured tomeasure the frequency response of the resonant circuit to determine themeasured resonant frequency.
 18. The apparatus of claim 1 wherein theresonant sense circuit is a first resonant sense circuit, wherein theresonant frequency is a first resonant frequency, wherein the couplingcircuit is a first coupling circuit, wherein the apparatus furthercomprises a second resonant sense circuit having a second resonantfrequency comprising a second electrically conductive structure, theapparatus further comprising a second coupling circuit, the detectioncircuit coupled to the second resonant sense circuit via themultiplexer, and wherein the detection circuit is configured to detectthe presence of the object further in response to detecting a differencebetween a second measured characteristic that depends on a frequency atwhich the second resonant sense circuit is resonating and acorresponding second characteristic that depends on the second resonantfrequency of the second resonant sense circuit, the second couplingcircuit further configured to reduce variation of the second resonantfrequency by the detection circuit in the absence of the object.
 19. Theapparatus of claim 18, wherein the first resonant frequency of the firstresonant sense circuit is different than the second resonant frequencyof the second resonant sense circuit.
 20. The apparatus of claim 18,wherein the first and second resonant sense circuits comprise a firstand a second loop, respectively, the first and second loopssubstantially co-planar.
 21. The apparatus of claim 20, wherein thefirst loop at least partially overlaps the second loop.
 22. Theapparatus of claim 1, wherein the coupling circuit provides at least oneof a weak coupling or a galvanic isolation between the resonant sensecircuit and the multiplexer.
 23. The apparatus of claim 1, furthercomprising at least one capacitor coupled between the multiplexer andthe detection circuit.
 24. A method for detecting a presence of anobject, the method comprising: applying a signal to a plurality ofresonant sense circuits, each having a resonant frequency, each resonantsense circuit coupled to a multiplexer and comprising a respective firstelectrically conductive structure and a coupling circuit configured todetermine resonance and an amount of coupling, the first electricallyconductive structures comprising a plurality of first loops collectivelydefining a first plane, and wherein the plurality of resonant sensecircuits and the multiplexer are coupled with at least one capacitortherebetween; wirelessly transmitting power via a second electricallyconductive structure different from the first electrically conductivestructures, the power transmitted via a magnetic field at a sufficientlevel to power or charge a load, the second electrically conductivestructure comprising a second loop defining a second plane substantiallyparallel with the first plane, the plurality of first loops at leastoverlapping an area enclosed by the second loop; and detecting thepresence of the object via a detection circuit coupled to themultiplexer in response to detecting a difference between a measuredcharacteristic that depends on a frequency at which the resonant sensecircuit is resonating and a corresponding characteristic that depends onthe resonant frequency of the resonant sense circuit.
 25. The method ofclaim 24, wherein the coupling circuit comprises one of: a capacitorelectrically connected between the electrically conductive structure andthe multiplexer, the resonant sense circuit comprising the capacitor andthe electrically conductive structure; at least one capacitor and acoupling loop electrically connected to the multiplexer, the couplingloop inductively coupled to the electrically conductive structure; or acapacitive voltage divider configured to capacitively couple themultiplexer to the resonant sense circuits.
 26. The method of claim 24,wherein the multiplexer and the detection circuit are coupled with atleast one capacitor therebetween.
 27. An apparatus for detecting apresence of an object, the apparatus comprising: a plurality of meansfor resonating at a plurality of resonant frequencies, the plurality ofresonating means positioned in a multi-dimensional array; means fordetermining resonance and an amount of coupling; means for multiplexingcoupled to the plurality of resonating means with at least one capacitortherebetween means for wirelessly transmitting power via a magneticfield at a level sufficient to power or charge a load; and means fordetecting the presence of the object in response to detecting adifference between a measured characteristic that depends on frequenciesat which each of the plurality of resonating means is resonating and acorresponding characteristic that depends on the resonant frequencies ofeach the plurality of resonating means.
 28. The apparatus of claim 27,wherein the determining means comprises one of: a capacitor electricallyconnected between the resonating means and the multiplexing means, theresonating means comprising the capacitor; at least one capacitor and acoupling loop electrically connected to the multiplexing means, thecoupling loop inductively coupled to the resonating means; or acapacitive voltage divider configured to capacitively couple themultiplexing means to the resonating means.
 29. An apparatus fordetecting a presence of an object, the apparatus comprising: a pluralityof sense circuits comprising respective electrically conductivestructures, the plurality of sense circuits including at least a firstsense circuit and a second sense circuit, the first sense circuitcomprising a first electrically conductive structure and forming a firstresonant circuit having a first resonant frequency, and the second sensecircuit comprising a second electrically conductive structure andforming a second resonant circuit having a second resonant frequencydifferent than the first resonant frequency; wherein the respectiveelectrically conductive structures each form respective loops, the loopspositioned in a multi-dimensional array defining a first plane; adetection circuit coupled to the first and second sense circuits, thedetection circuit configured to detect the presence of the object inresponse to detecting: a difference between a first measuredcharacteristic that depends on a frequency at which the first resonantcircuit is resonating and a first corresponding characteristic thatdepends on the first resonant frequency, or a difference between asecond measured characteristic that depends on a frequency at which thesecond resonant circuit is resonating and a second correspondingcharacteristic that depends on the second resonant frequency; and acoupling circuit coupled between the first and second sense circuits andthe detection circuit, the coupling circuit configured to reducevariation of the first and second resonant frequencies by the detectioncircuit in the absence of the object, wherein the first and second sensecircuits further comprise a first and second capacitor, respectively,the first and second capacitors each having values tuned to determinethe first and second resonant frequencies, respectively, wherein thecoupling circuit comprises a third capacitor coupled between thedetection circuit and the first and second sense circuits, at least thethird capacitor and the first capacitor forming a capacitive voltagedivider.
 30. The apparatus of claim 29, wherein the detection circuit isfurther configured detect a position of the object relative to at leastone of the first and second electrically conductive structures inresponse to the detecting.
 31. The apparatus of claim 29, wherein thefirst and second sense circuits each comprise a capacitor having a valuetuned to determine the first and second resonant frequencies,respectively.
 32. The apparatus of claim 29, wherein the couplingcircuit comprises: a coupling loop electrically connected the detectioncircuit, the coupling loop inductively coupled to the first and secondsense circuits, the first and second sense circuits substantially aloneforming the first and second resonant frequencies, respectively.
 33. Theapparatus of claim 29, wherein the first and second sense circuitscomprise a first and second capacitor, respectively, the first andsecond capacitors each having values tuned to determine the first andsecond resonant frequencies, respectively, wherein the coupling circuitcomprises a third capacitor coupled between the detection circuit andthe first sense circuit and a fourth capacitor coupled between thedetection circuit and the second sense circuit, the third capacitor andthe first capacitor forming a first capacitive voltage divider, and thefourth capacitor and the first capacitor forming a second capacitivevoltage divider.
 34. The apparatus of claim 29, wherein the apparatusfurther comprises a third electrically conductive structure, differentfrom the first and second electrically conductive structures, the thirdelectrically conductive structure configured to wirelessly transmitpower via a magnetic field at a level sufficient to power or charge aload.
 35. The apparatus of claim 34, wherein the first plane issubstantially parallel with a second plane defined by the thirdelectrically conductive structure, wherein the loops collectively coverat least an area covered by the third electrically conductive structure.36. The apparatus of claim 35, wherein at least each of the plurality ofsense circuits form respective resonant circuits having respectiveresonant frequencies, wherein the detection circuit is configured detectthe presence of the object in response to detecting a difference betweenrespective measured characteristics that depend on frequencies at whichthe respective resonant circuits are resonating and respectivecorresponding characteristics that depend on the respective resonantfrequencies.
 37. The apparatus of claim 29, wherein the first and secondmeasured characteristics are at least one of first and second measuredresonant frequencies or first and second measured quality factors(Q-factor) of the first and second resonant circuits.
 38. The apparatusof claim 29, wherein the first and second electrically conductivestructure comprise first and second loops, respectively, a diameter ofeach of the first and second loops substantially equal to or less thantwice a size of the object.
 39. An apparatus for detecting a presence ofan object, the apparatus comprising: a plurality of resonant sensecircuits, each having a resonant frequency, each resonant sense circuitcomprising an electrically conductive structure and a coupling circuitconfigured to determine resonance and an amount of coupling, theelectrically conductive structure comprising a loop positioned within amultidimensional loop array; a multiplexer coupled to the plurality ofresonant sense circuits; and a detection circuit coupled to themultiplexer, the detection circuit configured to detect the presence ofthe object in response to detecting a difference between a measuredcharacteristic that depends on a frequency at which a resonant sensecircuit of the plurality of resonant sense circuits is resonating and acorresponding characteristic that depends on the resonant frequency ofthe resonant sense circuit at least one capacitor coupled between themultiplexer and the detection circuit.